1.y=2-4x-x^2 =-(x+2)^2+6所以开口向下,顶点坐标是（-2,6）,对称轴是x=-2.2.y=-3/4x^2+6x-7 =-3/4(x-4)^2+5所以开口向下,顶点坐标是(4,5),对称轴是x=4.3.y=-2x^2-5x+7 =-2（x+5/4)^2+81/8所以开口向下,顶点坐标是(-5...