tana+seca
=sina/cosa+1/cosa
=(1+sina)/cosa
=[sin²(a/2)+cos²(a/2)+2sin(a/2)cos(a/2)]/[cos²(a/2)-sin²(a/2)]
=[cos(a/2)+sin(a/2)]²/[cos²(a/2)-sin²(a/2)]
=[cos(a/2)+sin(a/2)]/[cos(a/2)-sin(a/2)]
=[1+tan(a/2)]/[1-tan(a/2)]
=tan(a/2+π/2)