Prove the identity (cos^2 A)/(sin^2 A) + cos^2 A = 1/(sin^2

Prove the identity (cos^2 A)/(sin^2 A) + cos^2 A = 1/(sin^2 A) - sin^2 A. Hence find all angles between -90 and 90 which satisfy the equation cotan^2 x + cos^2 x + sin^2 x = 4/3.