图为二次函数y=ax05+bx+c的图像,给出下列说法:

按图,开口向上,a > 0
与轴的交点为(-1,0),(3,0),二次函数可表达为y = a(x + 1)(x - 3) = ax² -2ax -3a
b = -2a,c = -3a
(1) ab = a(-2a) = -2a² < 0,正确
(2) ax²+b+c=0,ax² = -(b + c) = -(-2a - 3a) = 5a,x² = 5,x = ±√5
(3) a + b + c = a - 2a - 3a = -4a < 0
(4) 对称轴为x = (-1 + 3)/2 = 1,x>1时,y随x值的增大而增大正确
(5) 显然,当y>0时,x < -1或x > 3