Question

：求证:(1-2sinθcosθ)/(cos2θ-sin2θ)=(cos2θ-sin2θ)/(1+2sinθcosθ).

Answer 1

证明：要证（1-2sinθcosθ)/(cos2θ-sin2θ)=(cos2θ-sin2θ)/(1+2sinθcosθ)成立只需证（1-2sinθcosθ)(1+2sinθcosθ)=(cos2θ-sin2θ)²成立；而（1-2sinθcosθ)(1+2sinθcosθ)=1-(2sinθcosθ)²=1...