y=√-x^2+x+2=√-(x^2-x+1/4)+2+1/4=√-(x-1/2)^2+9/4因为√-(x-1/2)^2+9/4》0,则,当x=2时,y有最小值,0当x=1/2时,y有最大值,3/2值域为[0,3/2]
