解分母
=2tan(π/4-a)sin^2(π/4+a)
=2cot[π/2-(π/4-a)]sin^2(π/4+a)
=2cot(π/4+a)sin^2(π/4+a)
=2cos(π/4+a)/sin(π/4+a)×sin^2(π/4+a)
=2cos(π/4+a)sin(π/4+a)
=sin(π/2+2a)
=cos2a
故原式=cos2a/cos2a=1.
解分母
=2tan(π/4-a)sin^2(π/4+a)
=2cot[π/2-(π/4-a)]sin^2(π/4+a)
=2cot(π/4+a)sin^2(π/4+a)
=2cos(π/4+a)/sin(π/4+a)×sin^2(π/4+a)
=2cos(π/4+a)sin(π/4+a)
=sin(π/2+2a)
=cos2a
故原式=cos2a/cos2a=1.