here a=2 b=2 nlogba=n
f(n)=nlogn
now f(n)/nlogba=logn
acc 2 basic master thm f(n) must b polynomial time smaller/greater than nlogba
but here it is greater by logn time so master thm not applied here
----but u can use extended master thm ie.
acc 2 this ans=theta(nlog2n)