Question

What is the value of f(5) for the function f(x) = 3x - 4?

Answer 1

f(5)= 3(5)-4
f(5)= 15-4
f(5)= 11

Answer 2

Thank you! I suck at functions..

Answer 3

Would you mind doing another one with me?

Answer 4

f(some number) just means to plug in that number wherever you see "x", and simplify. That will give you the function value, "evaluated at x".

@kdekle showed you how to do this above. Why not try your next problem yourself, and then just post what you did, and someone can tell you if you're right? I bet you can do it! :)

Answer 5

It has two letters now though, and i dont know where to begin.

What is the value of f[g(5)] for the functions f(x) = 2x + 1 and g(x) = 2x - 5?

Answer 6

Does x just equal five in both of them?

Answer 7

no you start from the inside and work out. so the inside says g(5). so Work out 2(5)-5. Now THAT answer is the x value in f.

Answer 8

OH! (:

Answer 9

That one looks a little bit different... but it isn't really. :) Just do it in two steps.

1. find g(5) (just like how you did f(5) above, except you'll use g(x) and plug in 5 for x)
2. Once you have g(5), which is just going to be some number, plug THAT number into f(x) for x and proceed as before! :)

Answer 10

2(5)-5
10-5
5



2(5)+1
10+1
11

?

Answer 11

exactly!

Answer 12

Awesome(: Thanks!!!
I wish i could give both of you medals):

Answer 13

Remember, when you see f(something) (or g(something) or t(something) or Q(something).... the point being, it does not matter what letter is used to "name" the function, that's just a name).....

what it means it to take the "rule" that is given to define f, and plug in the (something) for the variable.

So in this case, where you have f[g(5)], the "something" that is to go into f, is g(5). So first you need to find g(5), which you do by using the rule for g(x), with x=5. :)

Answer 14

You're welcome, and no problem, @kdekle got you started and I just gave an "assist", lol. :)