(1-sin^2x/cosx)= (sin2x/2sinx)
Left side:1-sin²(x) = cos²(x)1-sin²(x) / cos(x) = cos²(x) / cos(x) = cos(x)Right side:sin(2x) = 2 sin(x) cos(x)sin(2x) / 2 sin(x) = 2 sin(x) cos(x) / 2 sin(x) = cos x
