PQSR 是一个平行四边形。
P，Q 和 R 的坐标分别为 (0,2)，(6,8) 和 (10,2)。
求平行四边形 PQSR 的面积。 答：... : ... 平方单位

1. Find the coordinates of the fourth vertex $S$.

In parallelogram $PQSR$, opposite sides are equal and parallel.

From $Q(6,8)$ to $R(10,2)$, the movement is
$\begin{pmatrix}10-6\\2-8\end{pmatrix}=\begin{pmatrix}4\\-6\end{pmatrix}.$

So from $P(0,2)$ to $S$, use the same movement:
$S=(0+4,\,2-6)=(4,-4).$

2. Identify a suitable base and perpendicular height.

The side $PR$ is horizontal since $P(0,2)$ and $R(10,2)$ have the same $y$-coordinate.

So
$PR=10-0=10.$

The perpendicular height is the vertical distance from $Q(6,8)$ to the line $PR$, which is $y=2$:
$8-2=6.$

3. Calculate the area of the parallelogram.

Area of parallelogram $=$ base $\times$ height.

$\text{Area}=10\times 6=60.$