I've been stuck for hours trying to solve the recurrence T(n) = 7T(n/3) + n^2 + 2n by using case 3 of the master theorem.
I've done a good chunk of the proof, but currently stuck attempting to solve the regularity property af(n/b) <= cf(n).
I don't think this fits the case 3 requirements, but my best shot has been (7n^2 / 9) + (14n / 3) <= (7/9)n^2 + 2(14/3)n. This is true for all n, but I'm using 2 constants. What should I do to find the sole constant c which would satisfy case 3?