Finding (f of g)(3) where f(x) = √x and g(x) = x+1

[tecrekka]

Homework Statement

(f of g)

f(x)= sqrt/x

g(x) = x+1

Homework Equations

(f of g)(3)

The Attempt at a Solution

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

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

 

[ehild]

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

ehild

 

[tecrekka]

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

 

[Tedjn]

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

 

[tecrekka]

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

 

[Mark44]

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

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)).

 

[tecrekka]

OH! I see! Thank you very much.

 

[HallsofIvy]

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

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