Question

ABCD is a parallelogram. The sum of $\angle A$ and$\angle B$ is

• A. ${90}^0$
• B. ${180}^0$
• C. ${45}^0$

Answer 1

The correct option is B ${180}^0$

ABCD is a parallelogram.
$⟹\angle A=\angle C,\angle B=\angle D$
($\because$ opposite angles of parallelogram are equal)
Also, Sum of interior angles of a quadrilateral is ${360}^0$
$⟹\angle A+\angle B+\angle C+\angle D={360}^0$
$⟹\angle A+\angle B+\angle A+\angle B={360}^0$
$(\because \angle A=\angle C,\angle B=\angle D)$
$⟹2\angle A+2\angle B={360}^0$
$⟹\angle A+\angle B=\frac{{360}^0}{2}={180}^0$