Homework Help: F of g, simple

1. Jun 11, 2010

tecrekka

1. The problem statement, all variables and given/known data

(f of g)

f(x)= sqrt/x

g(x) = x+1

2. Relevant equations

(f of g)(3)

3. The attempt at a solution

sqrt/3 (4) = 4(sqrt/3) (incorrect)

Correct answer is 2 but I don't see how?

2. Jun 11, 2010

ehild

f(x)=sqrt/x has no sense. Is not it f(x)= sqrt(x)?

ehild

3. Jun 11, 2010

tecrekka

You are absolutely correct, sorry, I see now that I put it in improperly. I've made it harder^2

4. Jun 11, 2010

Tedjn

You are doing in your working (f * g), not (f of g). In the latter, you pass the result of g to f.

5. Jun 12, 2010

tecrekka

I'm just not seeing what you are saying for some reason, if (x)=3 don't I substitute every (x) with 3?

6. Jun 12, 2010

Staff: Mentor

No, not at all. To evaluate f(g(3)) you need to evaluate g(3), and then use that number in f.

For example, if g(3) = 5 -- I'm just making up numbers here -- then you would evaluate f(5). That would be f(g(3)).

7. Jun 12, 2010

tecrekka

OH!!! I see! Thank you very much.

8. Jun 12, 2010

HallsofIvy

I would say "yes, you do", but that $fog(x)= f(g(x))$ only has one x!

Last edited by a moderator: Jun 13, 2010