A parallelogram is a quadrilateral whose opposite sides are parallel and equal. The opposite sides being parallel and equal, forms equal angles on the opposite sides. Diagonals of a parallelogram are the segments which connect the opposite corners of the figure. 
Where,
p,q are the diagonals
a,b are the parallel sides
p=root a2+b2−2abcos(A) =roota2+b2+2abcos(B)
q=root a2+b2+2abcos(A) =√a2+b2−2abcos(B)
p2+q2=2(a2+b2)
Written on Feb. 3, 2021, 1:11 p.m.