Question

Assume f(x) = 2x + 8 and g(x) = 5. What is the value of (g o f)(3)?

Answer 1

This is the process I used and answer I got. Is it correct?
(g o f) (x)= g(f(x))
5(2x+8)
10x+40
3(10x+40)
30x+120

Answer 2

g(x) is not equal to 5x

g(x) is equal to 5

Answer 3

So I can't multiply 2x+8 by 5?

Answer 4

g(x) = 5

g(2x+8) = 5

g(2(3)+8) = 5

Answer 5

so it would be g(14)=5? Where do I go from there?

Answer 6

(g o f)(3)
= g(f(3))
= g(2(3)+8)
= g(14)
= 5

Answer 7

so 5 is the final answer?

Answer 8

yes

Answer 9

I understand that g(x) = 5 but how do you go from g(14) to 5? What's the point of the calculation if the answer given to you in the question?

Answer 10

The function g, takes an input (say x) and returns the number 5 every time.

This kind of question is useful if you are not use to the function(input) notation.

You might like to compare this result (g o f)(3), with the result of (f o g)(3)

and notice that they are quite different results.

Answer 11

Ok that makes sense. Thank you so much