Answer:

Explanation:
Recall the vertex form of a quadratic equation:

Where (h,k) is the vertex.
We are told that the vertex is (0,0). Therefore:

Simplify:

So, to finish the equation, we need to find a.
We know that a point is (2,1). Thus, substitute 1 for f(x) and 2 for x:

Square:

Divide both sides by 4:

So, our a value is 1/4.
And we can thus complete our equation:

And we are done :)