M2 Q. Tri. function 快 20分!

tan² A - 2 tan² B = 1sin²A / (1 - sin²A) - 2sin²B / (1 - sin²B) = 1sin²A (1 - sin²B) - 2sin²B (1 - sin²A) = (1 - sin²A)(1 - sin²B)sin²A - sin²A sin²B - 2sin²B + 2sin²B sin²A = 1 - sin²A - sin²B + sin²A sin²Bsin²A - 2sin²B = 1 - sin²A - sin²B1 - 2sin² A + sin² B = 0cos 2A + sin² B = 0


2011-03-02 23:20:58 補充：
tan² A = (sinA / cosA)² = sin²A/cos²A = sin²A / (1 - sin²A)

Thank you so much! >m