已知抛物线满足以下条件,求函数的表达式

1.
对称轴是直线x=2,与x轴的另一交点为(3,0)
y = a(x - 1)(x - 3)
过点B:-3 = a(0 - 1)(0 - 3),a = -1
y = -(x - 1)(x - 3) = -x² + 4x - 3
2.
顶点是(-2,3),抛物线:y = a(x + 2)² + 3
过点(-1,5):5 = a(-1+2)² + 3,a = 2
y = 2x² + 8x + 11
3.
与x轴的交点(-2,0),(4,0):y = a(x + 2)(x - 4)
过点(1,-9/2):-9/2 = a(1 + 2)(1 - 4),a = 1/2
y = x²/2 - x - 4
4.
对称轴是直线x=1,与x轴的交点:(-3,0),(5,0)
y = a(x + 3)(x - 5)
过点(1,16):16 = a(1 + 3)(1 - 5),a = -1
y = -x² + 2x + 15