更新时间2018-07-22 13:36:24
2,求2sin(π-α)+sin(2分之π-α)分之cos(-α)+4cos(2分之π+α)的值
cos(π+α)=5分之4即 -cosα=4/5, cosα=-4/5, sin²α=1-cos²α=1-16/25=9/25
又 因为 tanα>0,所以 α终边在第三象限,sinα=-3/5, tanα=sinα/cosα=3/4
2sin(π-α)+sin(2分之π-α)分之cos(-α)+4cos(2分之π+α)
=2sinα+cosα/cosα+4(-sinα)
=2(-3/5)+1+4*3/5
=11/5