f(n) = 2n - 1
for n = 1
2(1) - 1 = 1---------1st term
for n = 2
2(2) - 1 = 3-------2nd term
for n = 3
2(3) - 1 = 5-------3rd term
1,3,5
Substituting n = 3:-
third term = f(3) = 2(3) - 1
= 5 (answer)
