This is the basic and conceptual question from trigonometric ratios in which we have given A and B are acute angles such that tan A= 1/3 , tan B = 1/2 and tan( A +B) = tan A+ tanB / 1- tanA tanB
We have to prove that A+ B = 45°
RS Aggarwal, class 10, chapter 11, question no 16.
Hope it helps you.