The x-intercept of a line is the point at which it crosses the x-axis, so the value of y has to equal zero. By setting y equal to zero in the equation, it's easy to find the x-intercept.
- Write the equation of the line, if possible
If you know the slope of the line and the y-intercept, you can write it in slope-intercept form. For example, a line with a slope of 2 that crosses the y-axis at (0, 8) has the equation of y = 2x + 8.
- Substitute zero as the value for y
Because the x-axis has a value of 0 for y, the equation needs to be written as 0 = 2x + 8.
- Solve the equation by isolating x
Subtracting 8 from both sides of the linear equation leaves -8 = 2x. Solving the equation by dividing by 2 yields -4 as the x-intercept. If you want to check your work and have graph paper handy, chart the line out and note where it crosses the x-axis, and substitute it into the equation to solve. If the original equation is in standard form of ax + by = c, it's solved in the same manner.