Use the definitions of asymptotic notations to prove that

a$)T(n)=2n^2+6n,$ then $T(n)=O(n^2)$

b$)T(n)=2n^2+6n,$ then $T(n)=(n^2)$

c$)T(n)=2n^2+6n,$ then $T(n)=(n^2)$

d$)T(n)=2nlogn-4n+5,$ then $T(n)=(nlogn)$