asymptotic tight bound for quadratic functions

Question

In CLRS (Introduction to Algorithms by Cormen, Leiserson, Rivest, and Stein), for a function

f(n) = an² + bn

Answer 1

c1 and c2 can be chosen arbitrarily, as long as 0 < c1 < a and a < c2 < infinity. n0 is then calculated from this, so that the inequality 0 <= c1*n^2 <= an^2 + bn + c <= c2*n^2 is satisfied for all n>=n0.