It is given that A+B+C=π, then,
A2+B2+C2=π2
A2+B2=π2−C2
tan(A2+B2)=tan(π2−C2)
tanA2+tanB21−tanA2tanB2=cotC2
tanA2+tanB21−tanA2tanB2=1tanC2
tanA2tanC2+tanB2tanC2=1−tanA2tanB2
tanA2tanB2+tanB2tanC2+tanA2tanC2=1
If A+B+C=180°, prove that
tan(A/2)tan(B/2)+ tan(B/2)tan(C/2)+ tan(C/2)tan(A/2)= 1