I still feel so confused, but maybe if I give an example that is given in the book, I will understand what is going on.
Suppose that f is defined recursively by
f(0)=3
f(n+1)=2f(n)+3
Find f(1), f(2), f(3), f(4)
Solution:
f(1)=2f(0)+3=2X3+3=9
f(2)=2f(1)+3=2X9+3=21
Where does that 9 come from????