∵y=-2x²-4x+3 =-2﹙X²+2X﹚+3 =-2﹙X²+2X+1²-1²﹚+3=-2﹙X+1﹚²+5 ∴二次函数y=-2x²-4x+3的最大值是:当X=-1时,Y最大=5...