In this exercise I want to show the time complexity of this recursive function. I know by gauging n*log (n) you get 1 < d < 2 for d for the master theorem T(n) = a * T(n/b) + n^d. With that you get T(n) = O(n^3) here.
But I don't like that way, I wanted to solve this by substitution. You find my try on the second image. Where is my false? Sorry for German words, I'm from Germany but there ain't that much so I didn't translate them.
EDIT: I posted the master theorem I'm talking about. This theorem has already been proofed and holds for a > 0, b > 1, d >= 0.
