Упростить Cos4a-sin4a- cos2a

[latex]\cos 4a-\sin4a-\cos 2a=\cos^2 2a-\sin^2 2a-2\sin 2a\cos 2a-\cos 2a=[/latex] [latex]=(\cos^2 a - \sin^2 a)^2-4\sin^2 a\cos^2 a(\cos^2 a-\sin^2 a)-[/latex] [latex]-(\cos^2 a-\sin^2 a)=\cos^4 a -2\sin^2 a \cos^2 a + \sin^4 a -[/latex] [latex]-4\sin^2 a\cos^4 a+4\sin^4 a\cos^2 a[/latex]