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Maths Gcse Wjec-Eduqas Higher

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  1. Scatter-Graphs-And-Correlation Wjec-Eduqas Higher
    2 主题
  2. Cumulative-Frequency-And-Box-Plots Wjec-Eduqas Higher
    4 主题
  3. Histograms Wjec-Eduqas Higher
    3 主题
  4. Statistical-Diagrams- Wjec-Eduqas Higher
    6 主题
  5. Averages-Ranges-And-Data Wjec-Eduqas Higher
    8 主题
  6. Combined-And-Conditional-Probability Wjec-Eduqas Higher
    3 主题
  7. Tree-Diagrams- Wjec-Eduqas Higher
    1 主题
  8. Simple-Probability-Diagrams- Wjec-Eduqas Higher
    3 主题
  9. Introduction-To-Probability Wjec-Eduqas Higher
    3 主题
  10. Transformations Wjec-Eduqas Higher
    5 主题
  11. Vectors Wjec-Eduqas Higher
    6 主题
  12. 3D-Pythagoras-And-Trigonometry Wjec-Eduqas Higher
    1 主题
  13. Sine-Cosine-Rule-And-Area-Of-Triangles- Wjec-Eduqas Higher
    4 主题
  14. Pythagoras-And-Trigonometry Wjec-Eduqas Higher
    4 主题
  15. Area-And-Volume-Of-Similar-Shapes Wjec-Eduqas Higher
    1 主题
  16. Congruence-Similarity-And-Geometrical-Proof Wjec-Eduqas Higher
    5 主题
  17. Volume-And-Surface-Area- Wjec-Eduqas Higher
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  18. Circles-Arcs-And-Sectors- Wjec-Eduqas Higher
    2 主题
  19. Area-And-Perimeter- Wjec-Eduqas Higher
    4 主题
  20. Circle-Theorems Wjec-Eduqas Higher
    7 主题
  21. Bearings-Scale-Drawing-Constructions-And-Loci Wjec-Eduqas Higher
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  22. Angles-In-Polygons-And-Parallel-Lines Wjec-Eduqas Higher
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  23. Symmetry-And-Shapes Wjec-Eduqas Higher
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  24. Exchange-Rates-And-Best-Buys Wjec-Eduqas Higher
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  25. Standard-And-Compound-Units- Wjec-Eduqas Higher
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  26. Direct-And-Inverse-Proportion- Wjec-Eduqas Higher
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  27. Problem-Solving-With-Ratios Wjec-Eduqas Higher
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  28. Ratios Wjec-Eduqas Higher
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  29. Sequences Wjec-Eduqas Higher
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  30. Transformations-Of-Graphs- Wjec-Eduqas Higher
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  31. Graphing-Inequalities- Wjec-Eduqas Higher
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  32. Solving-Inequalities- Wjec-Eduqas Higher
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  33. Real-Life-Graphs Wjec-Eduqas Higher
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  34. Estimating-Gradients-And-Areas-Under-Graphs Wjec-Eduqas Higher
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  35. Equation-Of-A-Circle- Wjec-Eduqas Higher
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  36. Graphs-Of-Functions Wjec-Eduqas Higher
    6 主题
  37. Linear-Graphs Wjec-Eduqas Higher
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  38. Quadratic-Equations Wjec-Eduqas Higher
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  39. Linear-Equations- Wjec-Eduqas Higher
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  40. Algebraic-Proof Wjec-Eduqas Higher
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  41. Rearranging-Formulae Wjec-Eduqas Higher
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  42. Coordinate-Geometry- Wjec-Eduqas Higher
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  43. Functions Wjec-Eduqas Higher
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  44. Forming-And-Solving-Equations Wjec-Eduqas Higher
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  45. Iteration Wjec-Eduqas Higher
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  46. Simultaneous-Equations Wjec-Eduqas Higher
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  47. Algebraic-Fractions- Wjec-Eduqas Higher
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  48. Completing-The-Square Wjec-Eduqas Higher
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  49. Factorising Wjec-Eduqas Higher
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  50. Expanding-Brackets Wjec-Eduqas Higher
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  51. Algebraic-Roots-And-Indices Wjec-Eduqas Higher
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  52. Introduction-To-Algebra Wjec-Eduqas Higher
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  53. Using-A-Calculator Wjec-Eduqas Higher
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  54. Surds Wjec-Eduqas Higher
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  55. Rounding-Estimation-And-Bounds Wjec-Eduqas Higher
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  56. Fractions-Decimals-And-Percentages Wjec-Eduqas Higher
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  57. Simple-And-Compound-Interest-Growth-And-Decay Wjec-Eduqas Higher
    4 主题
  58. Percentages Wjec-Eduqas Higher
    3 主题
  59. Fractions Wjec-Eduqas Higher
    4 主题
  60. Powers-Roots-And-Standard-Form Wjec-Eduqas Higher
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  61. Prime-Factors-Hcf-And-Lcm- Wjec-Eduqas Higher
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  62. Number-Operations Wjec-Eduqas Higher
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Exam code:C300

Finding equations of straight lines

What is the equation of a straight line?

  • The general equation of a straight line is y = mx + c where

    • m is the gradient

    • c  is the y-intercept

      • The value where it cuts the y-axis

  • y = 5x + 2 is a straight line with

    • gradient 5

    • y-intercept 2

  • y = 3 – 4x is a straight line with

    • gradient -4

    • y-intercept 3

How do I find the equation of a straight line from a graph?

  • Find the gradient by drawing a triangle and using

    • gradient equals rise over run

      • Positive for uphill lines, negative for downhill

  • Read off the y-intercept from the graph

    • Where it cuts the y-axis

  • Substitute these values into y = mx + c 

What if no y-intercept is shown?

  • If you can’t read off the y-intercept

    • find any point on the line

    • substitute it into the equation

    • solve to find c 

  • For example, a line with gradient 6 passes through (2, 15)

    • The y-intercept is unknown

      • Write y = 6x + c

    • Substitute in x = 2 and y = 15

      • 15 = 6 × 2 + c

      • 15 = 12 + c

    • Solve for c

      • c  = 3

    • The equation is y  = 6x + 3

What are the equations of horizontal and vertical lines?

  • A horizontal line has the equation y = c

    • c is the y-intercept

  • A vertical line has the equation x  = k

    •  k is the x-intercept

  • For example

    • y = 4

    • x = -2

Worked Example

(a) Find the equation of the straight line shown in the diagram below.

Graph of a straight line with negative gradient

Find m, the gradient
Identify any two points the line passes through and work out the rise and run

Line passes through (2, 4) and (10, 0)

Finding the equation of a straight line from a graph

The rise is 4
The run is 8

Calculate the fraction rise over run

rise over run equals 4 over 8 equals 1 half

The slope is downward (downhill), so it is a negative gradient

gradient, <img alt=”m equals negative 1 half” data-mathml='<math ><semantics><mrow><mi >m</mi><mo >=</mo><mo >-</mo><mfrac ><mn>1</mn><mn>2</mn></mfrac></mrow><annotation encoding=”application/vnd.wiris.mtweb-params+json”>{“language”:”en”,”fontFamily”:”Times New Roman”,”fontSize”:”18″,”autoformat”:true}</annotation></semantics></math>’ data-type=”working” height=”47″ role=”math” src=”data:image/svg+xml;charset=utf8,%3Csvg%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20xmlns%3Awrs%3D%22http%3A%2F%2Fwww.wiris.com%2Fxml%2Fmathml-extension%22%20height%3D%2247%22%20width%3D%2267%22%20wrs%3Abaseline%3D%2230%22%3E%3C!–MathML%3A%20%3Cmath%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmi%20mathcolor%3D%22%23000000%22%3Em%3C%2Fmi%3E%3Cmo%20mathcolor%3D%22%23000000%22%3E%3D%3C%2Fmo%3E%3Cmo%20mathcolor%3D%22%23000000%22%3E-%3C%2Fmo%3E%3Cmfrac%20mathcolor%3D%22%23000000%22%3E%3Cmn%3E1%3C%2Fmn%3E%3Cmn%3E2%3C%2Fmn%3E%3C%2Fmfrac%3E%3C%2Fmath%3E–%3E%3Cdefs%3E%3Cstyle%20type%3D%22text%2Fcss%22%3E%40font-face%7Bfont-family%3A’math143f4d31b04031e49f5eb18baba’%3Bsrc%3Aurl(data%3Afont%2Ftruetype%3Bcharset%3Dutf-8%3Bbase64%2CAAEAAAAMAIAAAwBAT1MvMi7iBBMAAADMAAAATmNtYXDEvmKUAAABHAAAADxjdnQgDVUNBwAAAVgAAAA6Z2x5ZoPi2VsAAAGUAAAA%2FGhlYWQQC2qxAAACkAAAADZoaGVhCGsXSAAAAsgAAAAkaG10eE2rRkcAAALsAAAADGxvY2EAHTwYAAAC%2BAAAABBtYXhwBT0FPgAAAwgAAAAgbmFtZaBxlY4AAAMoAAABn3Bvc3QB9wD6AAAEyAAAACBwcmVwa1uragAABOgAAAAUAAADSwGQAAUAAAQABAAAAAAABAAEAAAAAAAAAQEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAACAgICAAAAAg1UADev96AAAD6ACWAAAAAAACAAEAAQAAABQAAwABAAAAFAAEACgAAAAGAAQAAQACAD0iEv%2F%2FAAAAPSIS%2F%2F%2F%2FxN3wAAEAAAAAAAAAAAFUAywAgAEAAFYAKgJYAh4BDgEsAiwAWgGAAoAAoADUAIAAAAAAAAAAKwBVAIAAqwDVAQABKwAHAAAAAgBVAAADAAOrAAMABwAAMxEhESUhESFVAqv9qwIA%2FgADq%2FxVVQMAAAIAgADrAtUCFQADAAcAZRgBsAgQsAbUsAYQsAXUsAgQsAHUsAEQsADUsAYQsAc8sAUQsAQ8sAEQsAI8sAAQsAM8ALAIELAG1LAGELAH1LAHELAB1LABELAC1LAGELAFPLAHELAEPLABELAAPLACELADPDEwEyE1IR0BITWAAlX9qwJVAcBV1VVVAAEAgAFVAtUBqwADADAYAbAEELEAA%2FawAzyxAgf1sAE8sQUD5gCxAAATELEABuWxAAETELABPLEDBfWwAjwTIRUhgAJV%2FasBq1YAAQAAAAEAANV4zkFfDzz1AAMEAP%2F%2F%2F%2F%2FWOhNz%2F%2F%2F%2F%2F9Y6E3MAAP8gBIADqwAAAAoAAgABAAAAAAABAAAD6P9qAAAXcAAA%2F7YEgAABAAAAAAAAAAAAAAAAAAAAAwNSAFUDVgCAA1YAgAAAAAAAAAAoAAAAsgAAAPwAAQAAAAMAXgAFAAAAAAACAIAEAAAAAAAEAADeAAAAAAAAABUBAgAAAAAAAAABABIAAAAAAAAAA

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