I have a problem that seems easy enough but i cant seem to find x and y

Problem: find a Parametrization for the graph of the function $\displaystyle y = x^2$

Starting at (3,9) and moving towards the origin,using angle$\displaystyle \theta$

in the accompanying figure as a parameter.

I drew out the graph and took a picture of it and i will include it.

I think i use $\displaystyle Tan \theta = \frac{y}{x} = \frac{9}{3} = 3$

Im not sure how to finish solving for x then to solve for y?

Im not sure if i need to find $\displaystyle y = mx + b$ since the slop comes out as zero?

Thank you..