3.4.1

Graphs of Common Functions

Test yourself

Common Functions

To sketch a graph, see if it is linear, quadratic or cubic. Then plot some x and y co-ordinates and join them up in the right shape.

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Linear

  • Linear functions are straight lines in the form y = mx + c.
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Quadratic

  • Quadratic functions have an x2 term.
  • They are in the form y = ax2 + bx + c.
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Cubic

  • Cubic functions are in the form y = ax3 + bx2 + cx + d.
  • If a > 0, it starts in the bottom left and goes up to the right.
  • If a < 0, it starts in the top left and goes down to the right.

Common Functions

To sketch a graph, look at whether it is exponential, reciprocal or some other type of graph. Then plot some x and y co-ordinates and join them up in the right shape.

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Exponential

  • Exponential functions are of the form y = kx or y = k-x.
  • They are completely above the x axis and go through the point (0, 1).
  • If k > 1 and the power is positive then the graph starts in the bottom left and then has a steep gradient up to the top right.
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Reciprocal

  • Reciprocal graphs never cross the x or y axis. They are only in 2 parts (quadrants) of the graph.
  • They are usually y = ax or xy = a.

Trigonometric Functions

To sketch trigonometric graphs (y = sin(x), y = cos(x), y = tan(x)) use x values which are multiples of 90° since these are the important points on the graph.

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Tangent

  • tan(x) repeats every 180°
  • There are vertical lines at 90°, 270°, ... because the function is undefined at these points.
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sin(x)

  • sin(x) repeats every 360°.
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sin(x) and cos(x)

  • cos(x) also repeats every 360°.
  • They have the same wave shape but the cosine graph is shifted by 90° compared to the sine graph.

Jump to other topics

1Numbers

2Equations, Formulae & Identities

3Sequences, Functions & Graphs

4Geometry

5Vectors & Transformation Geometry

6Statistics & Probability

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