A triangle has vertices A(2, 3), B(−1, 0) and C(2, −4). Find its area in square units.

A and C share the $x$-coordinate 2, so AC is vertical with length $3-(-4)=7$ units, and the perpendicular distance from B to the line $x=2$ is |$2-(-1)$| = 3 units. Area = ½ × $7\times 3=10.5$ square units.