由(-2,3), (4,3)这两个对称点,设y=a(x+2)(x-4)+3
当x=0时,y=-8a+3=-2
得;a=5/8
所以y=5/8(x+2)(x-4)+3=5/8(x^2-2x-8)+3=5/8x^2-5/4x-2