how to prove cos^2A(1+tan^2 A)=1

Answer 1

LS = cos^2 A (1 + sin^2 A/cos^2 A )
= cos^2 A (cos^2 A + sin^2 A)/cos^2 A , using a LCD
= cos^2 A (1/cos^2 A)
= 1
= RS