Given:ABCD is a quadrilateral in which AB parallel to CD and AD=BC=5 if ∠A=105º
We need to find the value of ∠B
From the properties of a parallelogram, we know that
Vertically opposite angles are equal.
Hence ∠A and ∠B forms Co interior angles and the sum of Co interior angles is 180º
∠A + ∠B= 180º
105 +∠B =180º