Big-O notation finding c and n0

Question

I\'ve just been introduced to Big-O notation and I\'ve been given some questions. However I\'m confused as to how to determine the value of n0. I have to show that

Answer 1

Divide by n^3 we get 3+20/n+5/n^3<=C 20/n+5/n^3<=C-3

Take C value as 10 20/n+5/n^3<=7

We need to solve this for different values of n until the condition gets satisfied C=10 and n0 = 3 will give the solution