(sina+sin2a)/(2cos2a+2sin^a+cosa)-tana
=sina(1+2cosa)/(2cos^a+cosa)-tana
=tana(1+2cosa)/(2cosa+1)-tana
=0
其中：cos2a=cos^a-sin^a2-2sin²a怎么变2cos²asin²a+cos²a=11-sin²a=cos²a∴2-2sin²a=2cos²a