[Solved]: Proof of big theta using induction

Problem Detail: Here is a recursive definition for the runtime of some unspecified function. $a$ and $c$ are positive constants. $T(n) = a$, if $n = 2$ $T(n) = 2T(n/2) + cn$ if $n > 2$ Use induction to prove that $T(n) = Theta(n log n)$ Any idea on how to solve this?

Asked By : Carol Doner

Answered By : Yuval Filmus

Hint: If $T(n/2) leq M frac{n}{2} log frac{n}{2}$ then $$ T(n) = 2T(n/2) + cn leq Mnlog frac{n}{2} + cn leq Mnlog n +n (c-Mlog 2). $$ The lower bound should be similar.
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