Question:
ABCD is a parallelogram in which ∠A = 70°. Compute ∠B, ∠C and ∠D.
Solution:
Opposite angles of a parallelogram are equal.
$\therefore \angle \mathrm{C}=70^{\circ}=\angle \mathrm{A} .$
$\angle \mathrm{B}=\angle \mathrm{D}$
Also, the sum of the adjacent angles of a parallelogram is $180^{\circ}$.
$\therefore \angle \mathrm{A}+\angle \mathrm{B}=180^{\circ}$
$70^{\circ}+\angle \mathrm{B}=180^{\circ}$
$\angle \mathrm{B}=110^{\circ}$
$\therefore \angle \mathrm{B}=110^{\circ}, \angle \mathrm{C}=70^{\circ}$ and $\angle \mathrm{D}=110^{\circ}$