若cos2x+cosx=0，则sin2x的值等于多少？

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cos2x+cosx=2cos�0�磨瞎5x-1+cosx=0
(cosx+1)(2cosx-1)=0
cosx=-1,cosx=1/2

cosx=-1
则x=2kπ+π
2x=4kπ+2π
所以枝蔽sin2x=0

cosx=1/2
x=2kπ+π/猛游州3,x=2kπ-π/3
2x=4kπ+2π/3,或2x=4kπ-2π/3
所以sin2x=sin2π/3=√3/2
或sin2x=sin-π/3=-√3/2

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cos2x+cosx=2cos²仔凳x-1+cosx=0
(cosx+1)(2cosx-1)=0
cosx=-1,cosx=1/2

cosx=-1
则败誉x=2kπ+π
2x=4kπ+2π
所以sin2x+sinx=0+0=0

cosx=1/2
x=2kπ+π/3,x=2kπ-π/3
2x=4kπ+2π/3,2x=4kπ-2π/3
所以sin2x+sinx=√3/2+√3/2=√3
或sin2x+sinx=-√3/2-√3/2=-√3

所以sin2x+sinx=0或察戚段√3或-√3

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正负四分之根号三或者是0~

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