y-intercept

Definition

The y-intercept is the point where a graph crosses the y-axis. Every point on the y-axis has x = 0, so you find the y-intercept by substituting x = 0. In y = mx + c, the y-intercept is (0; c).

Worked example

For y = 2x − 6, substituting x = 0 gives y = −6, so the y-intercept is (0; −6).

The x-intercept is found the other way round: set y = 0. For y = 2x − 6, 0 = 2x − 6 gives x = 3, so (3; 0).

Where it appears in the exam

y-intercept is part of the graphs section of CAPS Grade 9 Mathematics and appears in school tests and the end-of-year exam.

Step-by-step method

1. Substitute x = 0 into the equation.
2. Calculate y.
3. Write the answer as a point (0; y).

Common mistake

Mixing up the intercepts: for the y-intercept set x = 0, and for the x-intercept set y = 0.

Related graphs terms

• Gradient

Frequently asked questions

What does y-intercept mean in Grade 9 Maths?

The y-intercept is the point where a graph crosses the y-axis. Every point on the y-axis has x = 0, so you find the y-intercept by substituting x = 0. In y = mx + c, the y-intercept is (0; c).

When do you learn about y-intercept?

y-intercept is taught in the graphs section of CAPS Grade 9 Mathematics and is used again in Grades 10 to 12.

How do I practise questions involving y-intercept?

Snap a question that uses y-intercept into Snap&Learn with your grade set to Grade 9, or work through the Grade 9 topic guide and practice papers.