cos2x+cosx=2cos²x-1+cosx=0(cosx+1)(2cosx-1)=0cosx=-1,cosx=1/2cosx=-1则x=2kπ+π2x=4kπ+2π所以sin2x+sinx=0+0=0cosx=1/2x=2kπ+π/3,x=2kπ-π/32x=4kπ+2π/3,2x=4kπ-2π/3所以sin2x+sinx=√3/2+√3/2=...