已知tan=2,求cos^4(π/3+α）-cos^4（α-π/6）的值
问题描述：
已知tan=2,求cos^4(π/3+α）-cos^4（α-π/6）的值
答
tanα=2,根据万能公式,得cos2α=-3/5,sin2α=4/5;原式=cos^4(π/3+α）-cos^4（π/6-α）=cos^4(π/3+α）-sin^4（π/3+α）=cos^2(π/3+α）-sin^2（π/3+α）=cos(2π/3+2α）= -（cos2α)/2+根号3*sin2α/2=(3+4*...