A parallelogram has adjacent sides of 78 inches and 90 inches, and the angles between them is 35 degrees. Find the length of each of the diagonals.

Answer 1

the two diagonals d1 and d2 can be found using the law of cosines:

d1^2 = 78^2 + 90^2 - 2(78)(90)cos35°
d2^2 = 78^2 + 90^2 - 2(78)(90)cos145°
= 78^2 + 90^2 + 2(78)(90)cos35°