16Hit1600
AlgebraHardWhere a line through two points meets the x-axis

Algebra practice question

In the xy-plane, the line through the points (−2, 5) and (4, −1) crosses the x-axis at point P. What is the x-coordinate of P?

Answer: 3

Slope: (−1 − 5)/(4 − (−2)) = −6/6 = −1. Using (4, −1): y = −x + 3. On the x-axis y = 0, so x = 3.

Common wrong answers

If you answered 0
0 is the y-coordinate of P, not the x-coordinate; P is (3, 0).
If you answered 1
1 is the midpoint's x-coordinate, not where the line meets the axis.
If you answered -3
−3 has the wrong sign; y = −x + 3 gives x = 3 when y = 0.

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