Question

One angle of parallelogram is of 90°. Prove that all remaining angle are also 90°

Answer 1

here a parallelogram ABCD
m of angle A=90°

angle A+angle B=180---( adjacent angle are supplementary)
90+angle B=180
angle B=180-90
angle B=90°

similarly angle C=90°

measure of quadrilateral is 360
angle A+angle B+angle C+angle D=360
90+90+90+angle D=360
270+angle D=360
angle D=360-270
angle D=90°

this prove

Answer 2

opposite angles of parallelogram are of equal measure

one angle is 90° then its opposite angle is also 90°

therefore remaining angle are also 90°