解:y=1/(-x^2+x-2)=1/[-(x^2-x+(1/2)^2-(1/2)^2)-2]=1/[-(x-1/2)^2-7/4]所以-(x-1/2)^2-7/4∈(负无穷,-7/4]所以y=1/(-x^2+x-2)∈[-4/7.0)
y=1\-x^2+x-2y=-1/（x^2-x+1/4+7/4)=-1/[(x-1/2)^2+7/4]>=-4/7
X的范围没有?
