2三角函数题证明下列恒等式：（1）tan^2a×sin^2a=tan^2a-sin^2a(2)cosa+tana---------------=sinacosa/sina+1/cosa(3)cos^2a-sin^2a1-tana-----------------------=----------------1+2sinacosa1+tana

Question

2三角函数题
证明下列恒等式：
（1）tan^2a×sin^2a=tan^2a-sin^2a (2)cosa+tana
--------------- =sina
cosa/sina+1/cosa
(3) cos^2a-sin^2a 1-tana
----------------------- =----------------
1+2sinacosa 1+tana

Answer 1

(1)tan^2a×sin^2a=tan^2a×(1-cos^2a)=tan^2a-sin^2a(将sin^2a用1-coa^2a代换)(2)(cosa+tana)/(cosa/sina+1/cosa)=sina(cosa+tana)/(cosa+tana)=sina(分子分母同时乘以sina)(3)(cos^2a-sin^2a)/(1+2sinacosa)=(cosa...