Find the equation of a parabola where the vertix is at origin and the parabola opens to the left and passes through (-1,2).

Answer 1

vertex at (0,0) means

y = ax^2

So, plug in (-1,2) and you have

2 = a(-1)^2
a = 2

so,

y = 2x^2

Answer 2

My bad. opens to the left:

x = ay^2
-1 = a*2^2
a = -1/4

x = -1/4 y^2
or
y^2 = -4x

http://www.wolframalpha.com/input/?i=y^2+%3D+-4x