Jawabanmu

2014-01-04T00:12:36+07:00
(x_p,y_p)=(-2,0)
\\(x_1,y_1)=(0,-1)

y-y_p=a(x-x_p)^2\\
y-0=a(x-(-2))^2\\
y=a(x+2)^2

cari a dengan substitusi (x1,y1)
 y_1=a(x_1+2)^2\\
 -1=a(0+2)^2\\
-1=4a\\
a= -\frac{1}{4}

jadi 
y=a(x+2)^2
y= -\frac{1}{4}(x+2)^2