已知函数f(x)=cos^2x+sinx+a-1,若f(x)=0有实数解求a的取值范围

cos^2x+sinx+a-1=0有实数解,等价于a=1- cos^2x-sinx有实数解,即a的取值在函数g(x)= 1- cos^2x-sinx的值域内.g(x)= 1- cos^2x-sinx=sin^2x+sinx=(sinx+1/2)^2-1/4,Sinx=-1/2时,g(x)取到最小值-1/4.Sinx=1时,g(x)取到...