1、
原式=(1-cos^4a/sin^4a)*sin²a+cos²a/sin²a
=sin²a-cos^4a/sin²a+cos²a/sin²a
=sin²a+(cos²a-cos^4a)/sin²a
=sin²a-cos²a(1-cos²a)/sin²a
=sin²a-cos²asin²a/sin²a
=sin²a-cos²a
=-cos2a
2、
sinθ-cosθ=1/2
平方
sin²θ-2sinθcosθ+cos²θ=1/4
1-2sinθcosθ=1/4
sinθcosθ=3/8
原式=(sinθ-cosθ)(sin²θ+sinθcosθ+cos²θ)
=1/2*(1+3/8)
=-11/16