Answer:
Step-by-step explanation:
Let ABCD be the parallogram.
A,B,C and D are vertices in that order.
Since ABCD is a parallelogram, we get opposite sides are parallel
AB || CD
AD is a transversal making interior angles as A and D
By parallel lines properties we have A +D =180...i
Similarly since BC||AD, and AB is a transversal
Angle A+B =180...ii
We have from i and ii, Angle B = angle D
On the same grounds, as above, we can prove that
Angle A = Angle C
It follows that in a parallelogram opposite angles are equal.
