y=x^2-3x+4=(x-3/2)^2+4-9/4=(x-3/2)^2+7/4,顶点为(3/2,7/4),对称轴为x=3/2 y=2x^2-3x+1=2(x^2-3/2x)+1=2(x-3/4)^2+1-9/8=2(x-3/4)^2-1/8,顶点为(3/4,-1/8),对称轴为x=3/4
