Hello, fallingsky!

Rotate the axes so that the new equation contains no xy-term.

. .

Here is what I got so far: .

. . . . all correct so far!

i got to this far and plug in to the original equation and simplied it.

But I don't know what to do after that.

Do you recognize the equation?

Substitute:

.

. . . .

. . . .

This is a parabola, opening upward, vertex at the origin.