Straight lines, gradients and vertical intercepts
Construct a line from your own valid points, use signed coordinate rise and run, and interpret the vertical intercept within the original context.
Section 4 · Functions (all14rows linked;self-check practice)
Exam scope and assessment notes
Original selected rational straight-line teaching with four stages and eight tasks. Build lines from learner-chosen anchors using their original independent axis scales. Any distinct admitted rational anchors are accepted, including reversed orders and off-window points. Actual coordinate rise/run, not ratios of picture lengths, determines gradient. Retain positive, negative, fractional and zero gradients, a rearranged equation, and vertical/coincident contrasts. Actual construction never fills the separate gradient/intercept answer. Rate units and intercept units differ. Extending a mathematical line does not extend a context domain; a complete-line intercept outside the domain is not an admitted initial observation. A complete wrong attempt may study the explained reference without passing fixed comparisons. Written reasoning and model validity need human review. All14Functions source rows have reviewed structural teaching/practice links;other Mathematics B source gaps remain explicit in the current course map;the4Ilink requires this complete line-construction record and4Jalso requires all three original sparse-graph strands. The remaining Pearson curriculum is incomplete;broader symbolic and practical judgements still need review. No official marks,mastery,specialist approval or formal assessment readiness. Single Higher-tier linear4MB1,entry context2026/27only. ISBN9780435044107is metadata only;no verified book body,chapter/Hub mapping or MathematicsA/Foundation/modular inheritance.
Before you begin
- Exact signed fractions, ordered pairs, original axis scales and substitution into a numerical expression.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which coordinate quotient gives a nonvertical line’s gradient?
What you will learn
- Recognise a numerical equation in slope-intercept form and identify its gradient and vertical-axis intercept.
- Construct a line from any two distinct valid rational anchors using the original independent axis scales.
- Use signed coordinate differences consistently, including horizontal lines and reversed anchor orders.
- Keep rate units, intercept units, plotting windows and context restrictions distinct.
Straight lines: Worked
Each stage starts with blank work and separate answers. Choose any two distinct valid points on the given original line. Use signed coordinate differences in the same order. The graph does not fill any of your answer fields.
A positive run points right; a negative run points left. Rise uses the corresponding vertical change. Reversing both anchor orders preserves the gradient. The visual angle depends on the axis scales and cannot replace coordinate rise divided by run.
Task 1: construct and interpret a line
Original equation: y = (2)x + (-3)
Construct two distinct points satisfying y = (2)x + (-3). Record their signed coordinate differences, then independently identify the gradient and vertical-axis intercept. Explain what extending this line does and does not show. Dimensionless mathematical coordinates on the complete real line; no applied context restriction. Use dimensionless for the gradient unit and dimensionless for the intercept unit.
Horizontal axis: -6 to 6, step 1 dimensionless. Vertical axis: -8 to 8, step 2 dimensionless.
My actual line construction
Calculate two points from the original equation, then convert each coordinate to signed divisions using its original unit step. Record both pairs, the actual rise and run, and the complete-line vertical intercept. Use exact fractions rather than rounded coefficients. A horizontal line has zero rise; a vertical line has zero run and no finite gradient.
Construction status: Not recorded or changed; record again
My separate final answer
Give m, c, and the ordered pair of the vertical-axis intercept independently. Retain rate and intercept units. If the context excludes x = 0, the algebraic intercept does not become an admitted initial observation.
Separate answer status: Not recorded or changed; record again
Task 2: construct and interpret a line
Original equation: y = (-3/2)x + (4)
Construct two distinct points satisfying y = (-3/2)x + (4). Record their signed coordinate differences, then independently identify the gradient and vertical-axis intercept. Explain what extending this line does and does not show. Dimensionless mathematical coordinates on the complete real line; no applied context restriction. Use dimensionless for the gradient unit and dimensionless for the intercept unit.
Horizontal axis: -6 to 6, step 1 dimensionless. Vertical axis: -8 to 8, step 2 dimensionless.
My actual line construction
Calculate two points from the original equation, then convert each coordinate to signed divisions using its original unit step. Record both pairs, the actual rise and run, and the complete-line vertical intercept. Use exact fractions rather than rounded coefficients. A horizontal line has zero rise; a vertical line has zero run and no finite gradient.
Construction status: Not recorded or changed; record again
My separate final answer
Give m, c, and the ordered pair of the vertical-axis intercept independently. Retain rate and intercept units. If the context excludes x = 0, the algebraic intercept does not become an admitted initial observation.
Separate answer status: Not recorded or changed; record again
Record every current line construction.
Written explanations and the validity of a practical model need human review. These fixed comparisons do not award marks or mastery. This selected introduction does not complete any of the fourteen Functions source rows or establish specialist or formal assessment approval.
What a straight-line equation tells us
In y = mx + c, each real input x produces one output y. The coefficient m tells us how much the output changes for each one-unit change in the input. The constant c is the output at x = 0. A drawing helps connect these facts, but the meaning comes from coordinate units and the original equation.
Build and check a line
Choose two different x-values, calculate each y from the original equation, and retain both ordered pairs. Plot with the stated axis scales. Calculate rise and run from the same anchor order. Check a separate third input against the resulting rule. A pair of coincident points cannot determine a unique line.
Horizontal and vertical contrasts
When m = 0, all outputs equal c: the line is horizontal and its gradient is zero. A vertical line x = k has no finite gradient because its run is zero. It cannot be represented as a function y = mx + c. This contrast supports understanding and is not an additional invented syllabus requirement.
Interpret a model carefully
A rate carries output-units per input-unit; the vertical intercept carries output-units. Check whether the intercept input belongs to the context domain. Extending a geometric line changes neither the original domain nor the evidence supporting an applied model.
Sources for this lesson
Pause and explain
For y = −(3/2)x + 4, reverse both chosen anchors. What happens to the gradient?
Worked example
Construct and interpret the two original straight-line tasks. Choose any distinct anchors satisfying each original equation and context. Retain both original axis scales and give separate gradient/intercept answers. Task 1: Construct two distinct points satisfying y = (2)x + (-3). Record their signed coordinate differences, then independently identify the gradient and vertical-axis intercept. Explain what extending this line does and does not show. Dimensionless mathematical coordinates on the complete real line; no applied context restriction. Use dimensionless for the gradient unit and dimensionless for the intercept unit. Horizontal window -6 to 6, step 1 dimensionless; vertical window -8 to 8, step 2 dimensionless. Task 2: Construct two distinct points satisfying y = (-3/2)x + (4). Record their signed coordinate differences, then independently identify the gradient and vertical-axis intercept. Explain what extending this line does and does not show. Dimensionless mathematical coordinates on the complete real line; no applied context restriction. Use dimensionless for the gradient unit and dimensionless for the intercept unit. Horizontal window -6 to 6, step 1 dimensionless; vertical window -8 to 8, step 2 dimensionless.
Show the worked solution
- Task 1: These reference anchors are (0, -3) and (2, 1). They are examples; any distinct valid anchors must be accepted.
- Task 1: Use coordinate differences in the same order: run = 2 - (0) = 2; rise = 1 - (-3) = 4.
- Task 1: The gradient is rise/run = (4)/(2) = 2. Reversing the anchors reverses both signs and preserves this quotient.
- Task 1: Putting x = 0 into the original equation gives y = -3; the complete mathematical line meets the vertical axis at (0, -3).
- Task 1: Coordinate gradient is measured in y-units per x-unit. The drawn angle depends on display scales and does not determine the numerical gradient.
- Task 1: Extending the mathematical line does not by itself justify a real-world prediction beyond a stated context domain.
- Task 2: These reference anchors are (0, 4) and (2, 1). They are examples; any distinct valid anchors must be accepted.
- Task 2: Use coordinate differences in the same order: run = 2 - (0) = 2; rise = 1 - (4) = -3.
- Task 2: The gradient is rise/run = (-3)/(2) = -3/2. Reversing the anchors reverses both signs and preserves this quotient.
- Task 2: Putting x = 0 into the original equation gives y = 4; the complete mathematical line meets the vertical axis at (0, 4).
- Task 2: Coordinate gradient is measured in y-units per x-unit. The drawn angle depends on display scales and does not determine the numerical gradient.
- Task 2: Extending the mathematical line does not by itself justify a real-world prediction beyond a stated context domain.
Answer Task 1: m = 2 dimensionless; c = -3 dimensionless; complete-line vertical intercept (0, -3). The intercept is allowed by the stated context. Task 2: m = -3/2 dimensionless; c = 4 dimensionless; complete-line vertical intercept (0, 4). The intercept is allowed by the stated context. Any distinct admitted anchors on the original line are accepted; the reference anchors are examples. Written reasoning and model validity need human review.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Construct and interpret the two original straight-line tasks. Choose any distinct anchors satisfying each original equation and context. Retain both original axis scales and give separate gradient/intercept answers. Task 1: Construct two distinct points satisfying y = (0)x + (5). Record their signed coordinate differences, then independently identify the gradient and vertical-axis intercept. Explain what extending this line does and does not show. Dimensionless mathematical coordinates on the complete real line; no applied context restriction. Use dimensionless for the gradient unit and dimensionless for the intercept unit. Horizontal window -4 to 4, step 1 dimensionless; vertical window -6 to 6, step 3/2 dimensionless. Task 2: Construct two distinct points satisfying 2y=3x-4. Record their signed coordinate differences, then independently identify the gradient and vertical-axis intercept. Explain what extending this line does and does not show. Dimensionless mathematical coordinates on the complete real line; no applied context restriction. Use dimensionless for the gradient unit and dimensionless for the intercept unit. Horizontal window -4 to 4, step 1 dimensionless; vertical window -6 to 6, step 3/2 dimensionless.
Give me a hint
Choose two distinct admitted x-values, substitute each into the original equation, and preserve the original scales. Divide coordinate rise by coordinate run in one consistent anchor order. Determine the complete-line intercept by x = 0, then check the original context domain.
Compare my reasoning
- Task 1: These reference anchors are (0, 5) and (2, 5). They are examples; any distinct valid anchors must be accepted.
- Task 1: Use coordinate differences in the same order: run = 2 - (0) = 2; rise = 5 - (5) = 0.
- Task 1: The gradient is rise/run = (0)/(2) = 0. Reversing the anchors reverses both signs and preserves this quotient.
- Task 1: Putting x = 0 into the original equation gives y = 5; the complete mathematical line meets the vertical axis at (0, 5).
- Task 1: Coordinate gradient is measured in y-units per x-unit. The drawn angle depends on display scales and does not determine the numerical gradient.
- Task 1: Extending the mathematical line does not by itself justify a real-world prediction beyond a stated context domain.
- Task 2: These reference anchors are (0, -2) and (2, 1). They are examples; any distinct valid anchors must be accepted.
- Task 2: Use coordinate differences in the same order: run = 2 - (0) = 2; rise = 1 - (-2) = 3.
- Task 2: The gradient is rise/run = (3)/(2) = 3/2. Reversing the anchors reverses both signs and preserves this quotient.
- Task 2: Putting x = 0 into the original equation gives y = -2; the complete mathematical line meets the vertical axis at (0, -2).
- Task 2: Coordinate gradient is measured in y-units per x-unit. The drawn angle depends on display scales and does not determine the numerical gradient.
- Task 2: Extending the mathematical line does not by itself justify a real-world prediction beyond a stated context domain.
Task 1: m = 0 dimensionless; c = 5 dimensionless; complete-line vertical intercept (0, 5). The intercept is allowed by the stated context. Task 2: m = 3/2 dimensionless; c = -2 dimensionless; complete-line vertical intercept (0, -2). The intercept is allowed by the stated context. Any distinct admitted anchors on the original line are accepted; the reference anchors are examples. Written reasoning and model validity need human review.
Look for these in your work
- My chosen anchors satisfy the original equation and stated context.
- My division counts use the original separate axis scales.
- My signed coordinate rise and run use the same anchor order.
- My separate answer retains the gradient, ordered-pair intercept and their units.
- My explanation distinguishes the mathematical line from the supplied context and still needs human review.
Construct and interpret the two original straight-line tasks. Choose any distinct anchors satisfying each original equation and context. Retain both original axis scales and give separate gradient/intercept answers. Task 1: Construct two distinct points satisfying y = (-2/3)x + (5/2). Record their signed coordinate differences, then independently identify the gradient and vertical-axis intercept. Explain what extending this line does and does not show. Dimensionless mathematical coordinates on the complete real line; no applied context restriction. Use dimensionless for the gradient unit and dimensionless for the intercept unit. Horizontal window -6 to 6, step 3/2 dimensionless; vertical window -6 to 6, step 1/2 dimensionless. Task 2: Construct two distinct points satisfying y = (-4)x + (0). Record their signed coordinate differences, then independently identify the gradient and vertical-axis intercept. Explain what extending this line does and does not show. Dimensionless mathematical coordinates on the complete real line; no applied context restriction. Use dimensionless for the gradient unit and dimensionless for the intercept unit. Horizontal window -6 to 6, step 3/2 dimensionless; vertical window -6 to 6, step 1/2 dimensionless.
Give me a hint
Choose two distinct admitted x-values, substitute each into the original equation, and preserve the original scales. Divide coordinate rise by coordinate run in one consistent anchor order. Determine the complete-line intercept by x = 0, then check the original context domain.
Compare my reasoning
- Task 1: These reference anchors are (3, 1/2) and (-3, 9/2). They are examples; any distinct valid anchors must be accepted.
- Task 1: Use coordinate differences in the same order: run = -3 - (3) = -6; rise = 9/2 - (1/2) = 4.
- Task 1: The gradient is rise/run = (4)/(-6) = -2/3. Reversing the anchors reverses both signs and preserves this quotient.
- Task 1: Putting x = 0 into the original equation gives y = 5/2; the complete mathematical line meets the vertical axis at (0, 5/2).
- Task 1: Coordinate gradient is measured in y-units per x-unit. The drawn angle depends on display scales and does not determine the numerical gradient.
- Task 1: Extending the mathematical line does not by itself justify a real-world prediction beyond a stated context domain.
- Task 2: These reference anchors are (3, -12) and (-3, 12). They are examples; any distinct valid anchors must be accepted.
- Task 2: Use coordinate differences in the same order: run = -3 - (3) = -6; rise = 12 - (-12) = 24.
- Task 2: The gradient is rise/run = (24)/(-6) = -4. Reversing the anchors reverses both signs and preserves this quotient.
- Task 2: Putting x = 0 into the original equation gives y = 0; the complete mathematical line meets the vertical axis at (0, 0).
- Task 2: Coordinate gradient is measured in y-units per x-unit. The drawn angle depends on display scales and does not determine the numerical gradient.
- Task 2: Extending the mathematical line does not by itself justify a real-world prediction beyond a stated context domain.
Task 1: m = -2/3 dimensionless; c = 5/2 dimensionless; complete-line vertical intercept (0, 5/2). The intercept is allowed by the stated context. Task 2: m = -4 dimensionless; c = 0 dimensionless; complete-line vertical intercept (0, 0). The intercept is allowed by the stated context. Any distinct admitted anchors on the original line are accepted; the reference anchors are examples. Written reasoning and model validity need human review.
Look for these in your work
- My chosen anchors satisfy the original equation and stated context.
- My division counts use the original separate axis scales.
- My signed coordinate rise and run use the same anchor order.
- My separate answer retains the gradient, ordered-pair intercept and their units.
- My explanation distinguishes the mathematical line from the supplied context and still needs human review.
Construct and interpret the two original straight-line tasks. Choose any distinct anchors satisfying each original equation and context. Retain both original axis scales and give separate gradient/intercept answers. Task 1: Construct two distinct points satisfying y = (3)x + (7). Record their signed coordinate differences, then independently identify the gradient and vertical-axis intercept. Explain what extending this line does and does not show. Hypothetical service cost in USD against distance in kilometres;allowed distance0to12. Use USD/km for the gradient unit and USD for the intercept unit. Horizontal window 0 to 12, step 2 kilometres; vertical window 0 to 50, step 5 USD. Task 2: Construct two distinct points satisfying y = (-3/2)x + (18). Record their signed coordinate differences, then independently identify the gradient and vertical-axis intercept. Explain what extending this line does and does not show. Hypothetical temperature in degrees Celsius against time in minutes;model allowed only from2to8minutes,so the full-line intercept at0is not an admitted reading. Use degrees Celsius/minute for the gradient unit and degrees Celsius for the intercept unit. Horizontal window 0 to 10, step 2 minutes; vertical window 0 to 20, step 5 degrees Celsius.
Give me a hint
Choose two distinct admitted x-values, substitute each into the original equation, and preserve the original scales. Divide coordinate rise by coordinate run in one consistent anchor order. Determine the complete-line intercept by x = 0, then check the original context domain.
Compare my reasoning
- Task 1: These reference anchors are (2, 13) and (6, 25). They are examples; any distinct valid anchors must be accepted.
- Task 1: Use coordinate differences in the same order: run = 6 - (2) = 4; rise = 25 - (13) = 12.
- Task 1: The gradient is rise/run = (12)/(4) = 3. Reversing the anchors reverses both signs and preserves this quotient.
- Task 1: Putting x = 0 into the original equation gives y = 7; the complete mathematical line meets the vertical axis at (0, 7).
- Task 1: Coordinate gradient is measured in y-units per x-unit. The drawn angle depends on display scales and does not determine the numerical gradient.
- Task 1: Extending the mathematical line does not by itself justify a real-world prediction beyond a stated context domain.
- Task 2: These reference anchors are (2, 15) and (6, 9). They are examples; any distinct valid anchors must be accepted.
- Task 2: Use coordinate differences in the same order: run = 6 - (2) = 4; rise = 9 - (15) = -6.
- Task 2: The gradient is rise/run = (-6)/(4) = -3/2. Reversing the anchors reverses both signs and preserves this quotient.
- Task 2: Putting x = 0 into the original equation gives y = 18; the complete mathematical line meets the vertical axis at (0, 18).
- Task 2: Coordinate gradient is measured in y-units per x-unit. The drawn angle depends on display scales and does not determine the numerical gradient.
- Task 2: A complete mathematical line can extend beyond the drawing; a contextual model remains restricted to its stated domain. In the temperature task, x = 0 lies outside 2 ≤ x ≤ 8, so the intercept is algebraically defined but not an admitted temperature observation.
Task 1: m = 3 USD/km; c = 7 USD; complete-line vertical intercept (0, 7). The intercept is allowed by the stated context. Task 2: m = -3/2 degrees Celsius/minute; c = 18 degrees Celsius; complete-line vertical intercept (0, 18). The intercept is outside the admitted context domain. Any distinct admitted anchors on the original line are accepted; the reference anchors are examples. Written reasoning and model validity need human review.
Look for these in your work
- My chosen anchors satisfy the original equation and stated context.
- My division counts use the original separate axis scales.
- My signed coordinate rise and run use the same anchor order.
- My separate answer retains the gradient, ordered-pair intercept and their units.
- My explanation distinguishes the mathematical line from the supplied context and still needs human review.
Common mistakes
- Using a ratio of screen lengths instead of coordinate rise divided by coordinate run.
- Changing the order for rise without changing it for run.
- Reading the constant from an equation before isolating y.
- Using coincident points to claim a unique line.
- Giving a vertical line a finite gradient.
- Rounding an exact fractional gradient.
- Confusing a rate unit with an intercept unit.
- Calling a mathematical intercept an observed initial value when the context excludes zero.
- Extending a real-world model without evidence when extending its mathematical line.
What can you explain now?
A temperature model is allowed only for times 2 to 8 minutes. Its complete mathematical line has intercept (0,18). Is 18 an admitted initial observation?
Compare with the explanation
No. The mathematical intercept is defined, but time 0 is outside the supplied model domain.
Substitution at x = 0 locates the complete-line intercept; it does not remove the domain restriction or establish an observed physical temperature.
After trying it yourself, choose your next review. This is your self-assessment.
Your review choice appears on Today. Sign in to sync it across devices.
Make it stick
Close the reference. Construct two distinct admitted points from the original equation, retain their signed coordinate rise and run and the independent axis scales, identify the exact gradient and ordered-pair vertical intercept, then justify the units and the original context domain.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.