WAEC 2022 · Paper 1 · Q40

The length of the line joining points $(x, 4)$ and $(-x, 3)$ is 7 units. Find the value of $x$ .

Worked solution (try it first)

By the distance formula, $(x - (-x))^2 + (4 - 3)^2 = 7^2$ , so $(2x)^2 + 1 = 49$ .
$(2x)^2 = 4x^2$ , so $4x^2 = 48$ and $x^2 = 12$ .
$x = \sqrt{12}$
$= \sqrt{4 \times 3}$
$= 2\sqrt{3}$ , option D.