Points A,B,C and D are chosen on a semicircle and quadrilateral ABCD is drawn.
Then tan A + tan B + tan C + tan D is
0
1.A,B,C,D lie on the circumference of a semi circle i.e on a circle. ∴ ABCD is a cyclic quadrilateral.
Hence sum of opposite angle is π, i.e., C = π - A, D = π - B.
tan A + tan B + tan C + tan D
= tan A + tan B + tan(π - A)+tan( π - B) = 0