In a rectangular trapezoid, the bases are 5 and 9, and one of the corners is 120. Find the large side.

Let’s build the height of the CH trapezoid of AВСD. In the right-angled triangle СDН, we determine the values of acute angles. DCH angle = (ВСD – ВСН) = (120 – 90) = 30.
Quadrangle ABCН is a rectangle, since the trapezoid is rectangular, and CH is its height, then AH = BC = 5 cm.Then DН = AD – AH = 9 – 5 = 4 cm.
The leg of the DН of the right-angled triangle СDН is located opposite the angle of 300, then СD = 2 * CH = 2 * 4 = 8 cm.
Answer: The large side is 8 cm.