Question

ABCD is a parallelogram with $\angle$ABC $={90}^{\circ }$, then number of right angles in the parallelogram excluding $\angle$ABC is/are ____

Answer 1

ABCD is the given parallelogram.

In a parallelogram, opposite internal angles are equal.

So $\angle$ABC $=\angle$ADC $={90}^{\circ }$

Also, $\angle$BAD $=\angle$BCD

In a quadrilateral, sum of all internal angles is ${360}^{\circ }$.

So, $\angle$BAD $+\angle$BCD $={180}^{\circ }$.

Therefore, $\angle$BAD $=\angle$BCD $={90}^{\circ }$.

So, the number of internal right angles is four and excluding $\angle$ABC it will be three.