y=2x的2次方-3x+5
y=2(x^2-3/2x)+5
y=2(x^2-3/2x+(3/4)^2-(3/4)^2)+5
y=2(x-3/4)^2-9/8+5
y=2(x-3/4)^2 +31/8
x的取值范围可以是任何实数,
yx的取值范围是y>=31/8x可取0吗x=0y=5