16Hit1600
AlgebraEasyFinding the x-intercept of a line

Algebra practice question

In the xy-plane, the graph of the equation y = 4x − 12 crosses the x-axis at the point (a, 0). What is the value of a?

Answer: 3

A point on the x-axis has y = 0. Substituting gives 0 = 4a − 12, so 4a = 12 and a = 3. (A common error is reporting −12, the y-intercept, instead of solving for the x-value where y = 0; another is dividing 12 by 4 incorrectly or answering 12.)

Common wrong answers

If you answered 12
You solved 4a = 12 but didn't divide by 4; a = 3.
If you answered -12
−12 is the y-intercept (the value of y when x = 0). For the x-intercept, set y = 0 and solve 0 = 4a − 12, giving a = 3.
If you answered -3
Check your sign: 0 = 4a − 12 gives 4a = +12, so a = 3.

More Algebra questions

Not affiliated with the College Board. SAT is a trademark of the College Board.