Question

in isosceles triangle ABC,AB=AC.the side BA is produced to D such that BA=AD.prove that:angleBCD=90degree

Answer 1

since
ab=ac=ad
then
angB=angACB=angACD=angD=X
WE KNOW THAT IN TRIANGLE PBC
X+2X+X=180
4X=180
X=45
THEREFORE
angc=x+x=2x=x*45=90
hence proved

Answer 2

Given ab=ac=ad AngleB=angleACB=angleACD=angleD=X In triangle PBC X+2X+X=180 4X=180 X=45 Therfore angleC=X+X=2x=x*45=90 Proved