What is the Result of Plugging g(x) Into f(x)?

[mathdad]

The question wants (f•g)(x). I understand this to be
f(g(x)).

This means to plug the value of g(x) into every x I see in f(x) and simplify.

f(3x^2) = 4(3x^2) + 7

f(3x^2) = 12x^2 + 7

So, f(g(x)) = 12x^2 + 7.

This is not the book's answer.

 

[topsquark]

The question wants (f•g)(x). I understand this to be
f(g(x)).

This means to plug the value of g(x) into every x I see in f(x) and simplify.

f(3x^2) = 4(3x^2) + 7

f(3x^2) = 12x^2 + 7

So, f(g(x)) = 12x^2 + 7.

This is not the book's answer.

What are your functions f(x), g(x)? Can't help you if we don't know that! Please give us the whole problem.

-Dan

 

[mathdad]

f(x) = 4x + 7

g(x) = 3x^2

 

[skeeter]

f(x) = 4x + 7

g(x) = 3x^2

So, f(g(x)) = 12x^2 + 7.

This is not the book's answer.

For the two functions you cite, your solution is correct ... what is the "book answer" ?

 

[mathdad]

Book's answer:

12x^2+21x.