if tan A/2 =cosecA-sin A then prove cos^2

Question

A/2=cos 36 degree

Answer 1

tan A/2 = (1-cosA)/sinA

So, you have

(1-cosA)/sinA = 1/sinA-sinA = (1-sin^2A)/sinA = cos^2A/sinA
so
cos^2A+cosA-1 = 0

Solve that for cosA, and then use the fact that

cos36° = (1+√5)/4

to prove the result

Answer 2

That is negetive and posetive