y=-3x^2+12x-3= -3(x-2)^2 + 9
y=－3x²＋12x－12＋9 =－3(x²－4x＋4)＋9 =－3(x－2)²＋9
y=-3x^2+12x-3 =-3（x-4x+4）+12-3 =-3（x-2）²+9
