2sin^2x+cosx-1=0
问题描述：
2sin^2x+cosx-1=0
答
2sin^2x+cosx-1=0
2-2cos^2x+cosx-1=0
2cos^2x-cosx-1=0
(2cosx+1)(cosx-1)=0
cosx=-1/2
cosx=1
x1=2kPai+2Pai/3
x2=2kPai
答
2sin^2x+cosx-1=0
2(1-cos^2x)+cosx-1=0
-2cos^2x+cosx+1=0
-(2cosx+1)(cosx-1)=0
cosx=1或cosx=-1/2
x=2kπ
或
x=2/3π+2kπ或4/3π+2kπ
答
2sin^2x+cosx-1=0
（1-cos^2x）*2+cosx-1=0
2cos^2x-cosx-1=0
cosx=1或cosx=-1/2
x=kπ或x=(2/3)π+kπ(k=0,1,2……)