Sin^4 a - cos^4 a - sin ^2 a + cos ^2 a

Question

Sin^4 a - cos^4 a - sin ^2 a + cos ^2 a

Answer 1

= (Sin^2 a - Cos^2a)(Sin^2 a + Cos^2 a) -Sin^2 a + Cos^2a = Sin^2 a - Cos^2 a  - Sin ^2 a+ Cos 2a= 0