A parallelogram has adjacent sides 60 $m$ and 25 $m$, and one of its diagonals is 65 $m$. Find its area in $m^2$.

The diagonal splits the parallelogram into two congruent triangles of sides 60, 25 and 65 m. Since $60^2+25^2=3600+625=4225=65^2$, each triangle is right-angled with area ½ × $60\times 25=750{\text{m}}^2$. Total area = $2\times 750=1500{\text{m}}^2$.