Question

if A,B,C are interior angles of triangle,show that sec^2 (b+c/2)-1=cot^2 A/2

Answer 1

A+B+C = 180°
or, (B+C)/2=90-A/2
or, sec(B+C)/2 = sec 90-A/2
or, sec(B+C)/2 = cosec A/2
or, sec²(B+C)/2 = cosec² A/2
or, sec² (B+C)/2-1 = cosec² A/2 -1
= cot² A/2