已知sina=2cosa.求sina-4cosa/5sina+2cos及sin平方a+2sinacosa的值

问题描述:

已知sina=2cosa.求sina-4cosa/5sina+2cos及sin平方a+2sinacosa的值

sina=2cosa...∴tana=2
(1)(sina-4cosa)/(5sina+2cos)
=(tana-4)/(5tana+2)
=-1/6
(2)sin^2a+2sinacosa
=(sin^2a+2sinacosa)/(sin^2a+cos^2a)
=(tan^2a+2tana)/(tan^2a+1)
=8/5