Linear Inequalities in Two Variables
y-intercept
The point where a graph crosses the y-axis.
| English | y-intercept |
|---|---|
| Bahasa Melayu | Pintasan-y |
| 中文 | y 轴截距 |
How it is used
For the boundary line y = 2x + 1, the y-intercept is 1, so the line crosses the y-axis at (0, 1); substituting x = 0 into the equation gives y = 1.
Where it shows up in SPM
Used when drawing the boundary line of an inequality: knowing the y-intercept and gradient lets you plot the line quickly. It also appears throughout Straight Lines and Graphs of Functions, and in Paper 1 items reading c from y = mx + c.
Don't confuse it with
Open the chapter: Linear Inequalities in Two Variables →
Frequently asked questions
How do I find the y-intercept from an equation that is not in y = mx + c form?
Substitute x = 0 and solve for y. For 2x + 3y = 12, putting x = 0 gives 3y = 12, so y = 4; the y-intercept is 4 and the line passes through (0, 4).
This works for any linear equation.
Why is the y-intercept useful when shading an inequality?
The boundary of the inequality is a straight line, and you need at least two points to draw it. The y-intercept gives one point instantly at (0, c); pair it with the x-intercept or the gradient to draw the line, then decide which side to shade.