二次函數的圖像

y=a(x-h)^2-8
=a(x^2-2xh+h^2)-8
=ax^2-2axh+ah^2-8
when y=0,x=-4 or 0
0=a(-4)^2-2(-4)ah+ah^2-8_________________________(1)
0=a(0)^2-2(0)ah+ah^2-8__________________________(2)

16a+8ah+ah^2-8=0
a(16+8h+h^2)=8
a=8/(16+8h+h^2)_______________________________(3)
putting (3) into (2)
ah^2-8=[8/(16+8h+h^2)]h^2-8=0
(8h^2)/(16+8h+h^2)=8
8h^2=128+64h+8h^2
64h+128=0
h=-2_______________________________(4)
putting (4)into (2)
ah^2-8=a(-2)^2-8=0
4a=8
a=2

any figure??