Question

if ABCD is a trapezium with AB parallel to DC if angle A is 50 degrees and angle B 65 degrees then angle DCB

Answer 1

Angle B and Angle DCB are supplementary
hence

Angle DCB = 115 DEGREES

Answer 2

Here, angleDCB+angleB=180(angles on the same side of transversal BC of parallel sides AB and DC)
angleDCB+65=180
angleDCB=180-65
angleDCB=115degree

angleDCB=115 degree