求y=cosx+sin^2x+1的最值
问题描述：
求y=cosx+sin^2x+1的最值
答
y=cosx+sin^2x+1
=cosx+1-cos^2x+1
=-cos^2x+cosx+2
=-(cos^2x-cosx+1/4)+9/4
=-(cosx-1/2)^2+9/4
因此
当cosx=1/2时有最大值9/4
当cosx=-1时有最小值0