Linear Equations in Two Variables
An equation like Ax + By = C describes every point on a line. Drag the sliders to see how changing A, B, and C moves where the line crosses each axis.
Instead of slope-intercept form, equations are often given in standard form, Ax + By = C. Rather than graphing from slope and y-intercept, it’s often faster to plot two points: the x-intercept (where the line crosses the x-axis, so y = 0) and the y-intercept (where it crosses the y-axis, so x = 0).
To find the x-intercept, set y = 0 and solve for x. To find the y-intercept, set x = 0 and solve for y. Once you have both points, you can draw the whole line — or check whether a given point lies on it by substituting and confirming both sides match.
The SAT frequently asks for one of these two intercepts directly, or gives you an intercept and asks you to find a missing coefficient — both are just a matter of setting the right variable to zero.