2/3+siny-cos²x=4/3-sinx-cos²x=sin²x-sinx+1/3=(sinx+1/2)²+1/12∵-1≤sinx≤1∴1/12≤(sinx+1/2)²+1/12≤7/32/3+siny-cos²x取值范围是[1/12,7/3]