enter image description here To prove $T(n) = \Theta(n^2)$ , it is necessary to simultaneously prove $T(n) = O(n^2)$ and $T(n) = \Omega(n^2)$ .
But I don't have any clue about proving $T(n) = \Omega(n^2)$, could you help me? Or there may be any other methods?
I have proved $T(n) = O(n^2)$ using Mathematical induction.