已知tanα=2,求值
问题描述：
已知tanα=2,求值
（2-2sin(α+3π/4)cos(α+π/4))/cos^4α-sin^4α）
答
2-2sin(α+3π/4)cos(α+π/4)=2-2(sin(2a+π)+sinπ/2)=2+2sin2a-2=2sin2acos^4α-sin^4α=(cos^2a+sin^2a)(cos^2a-sin^2a)=cos^2a-sin^2a=cos2a（2-2sin(α+3π/4)cos(α+π/4))/cos^4α-sin^4α）=2sin2a/cos2a=2...