3.3.2

Straight Line Graphs

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Straight Line Graphs

Any straight line can be written as y = mx + c.

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y = mx + c

  • m is the gradient of the line
  • c is the y-intercept (the height of the point where the line crosses the y axis.
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Parallel lines have the same gradient

  • y = 3x + 2 and y = 3x - 4 are parallel lines because they have the same gradient (3).

Gradient and y-intercept of a Line

A line y = mx + c has gradient m and y-intercept c.

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y-intercept

  • The point where a line crosses the y-axis is called the y-intercept.
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Gradient

  • To calculate the gradient (slope) of a line, use 2 co-ordinates (A and B):
    • gradient = change in y ÷ change in x
    • where change in y = (yA - yB) and change in x = (xA - xB)

Midpoint of a Line

The midpoint of a line is the point that lies the same distance from each of the endpoints.

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Midpoint

  • To calculate the coordinates of the midpoint between points A and B, work out the horizontal distance between A & B and add half of this to the x-coordinate of A.
  • This is the x-coordinate of the midpoint.
  • Do the same for the vertical distance to get the y-coordinate.
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Midpoint formulae

  • The coordinates of the midpoint of a line AB are given by the formulae above.

Jump to other topics

1Numbers

2Equations, Formulae & Identities

3Sequences, Functions & Graphs

4Geometry

5Vectors & Transformation Geometry

6Statistics & Probability

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