Question

if A,B,C,D is the angle of quadrilateral, then show that sin(A+B+C)+sin(A+B+C+2D)=0

Answer 1

A+B+C=180°
Sin (A+B+C) =Sin 180=0
A+B+C+D=360°
sin(A+B+C+2D)+Sin(360+180)=sin180=0
Sin(A+B+C)+Sin(A+B+C+2D)=0