To obtain the inverse fucntion basically all we have to do is re-arrange the equation and the do a small trick of swaping x and f(x), which can be done either at the start or at the end.
We must first remember that to integrate, we must increase the power by 1 and divide by this new power.
Therefore, to integrate 3x^2 + 4x + 9, we take the first term, 3x^2