sin4x/[4sin^2(π/4+x)tan(π/4-x)]
=sin4x/[4sin^2(π/4+x)tan[π/2-(π/4+x)]
=sin4x/[4sin^2(π/4+x)tan[π/2-(π/4+x)]
=sin4x/[4sin^2(π/4+x)cot(π/4+x)
=sin4x/[4sin^2(π/4+x)cos(π/4+x)/sin(π/4+x)
=sin4x/4sin(π/4+x)cos(π/4+x)
=sin4x/2sin(π/2+2x)c
=sin4x/2sin(π/2+2x)
=sin4x/2cos2x
=2sin2x2cos2x/2cos2x
=2sin2x
2)
求答案的同时自己也要去思索啊 现在的学生真的是!