Data Structures, Algorithms, & Applications in C++
Chapter 3, Exercise 5

(a)

2n + 7 is asymptotically smaller than n2. Therefore, 2n + 7 != Omega(n2).

(c)

5n3 + 6n2 is asymptotically smaller than n3log n. Therefore, 5n3 + 6n2 != Omega(n3log n).