Question

prove that the opposite angles of a parallelogram are equal.

Answer 1

In parrelogram AB is parallel to its opposite side DC and side AD is parallel to its opposite side BC. Therefore, ABCD is a parrelogram.

Answer 2

LET. ABCD is a parallelogram

angle A = angle C and AD || BC

as sum of consecutive angles

angle B + angle A = 180

angle B + 40 = 180

angle B = 180- 40

angle B = 140

in a parallelogram opposite sides are equal

A = C = 40 , B =D = 140

opposite sides are equal