1. ## Functions

$Given: f(x)=2x+f(x-1) and f(1)=4, find f(9)$ (sorry guys, latex is being uncooperative. towards the end that says: and f(1)=4, find f(9).)

Could anyone suggest where i might begin this problem?

2. Originally Posted by rtblue
$Given: f(x)=2x+f(x-1) and f(1)=4, find f(9)$ (sorry guys, latex is being uncooperative. towards the end that says: and f(1)=4, find f(9).)

Could anyone suggest where i might begin this problem?
The function is define recursively

Notice that

$f(2)=2(2)+f(2-1)=4+f(1)=4+4=8$ and now

$f(3)=2(3)+f(2)=6+8=...$

3. Or, work backwards:
f(9)= 2(9)+ f(8)= 18+ (2(8)+ f(7))= 18+ 16+ (2(7)+ f(6)), etc.

(It's generally not a good idea to put text into LaTex. If you didn't mean to then you probably missed the [/ math] at the end.)