General equation of parabola: y-k = a(x-h)^2
Here the vertex is at (0,0), so we have y-0 = a(x-0)^2, or y = ax^2
All we have to do now is to find the value of the coefficient a.
(1,2) is on the curve. Therefore, 2 = a(1)^2, or 2 = a(1), or a = 2.
The equation of this parabola is y = 2x^2.