Question

am I right at all?

Given that f(x) = 2x + 5 and g(x) = x − 7, solve for f(g(x)) when x = −3.

−15 << my answer
−8
10
25

Answer 1

@FrostFlare23 mind showing the work you did to arrive at that answer?

Answer 2

alright give me a second

Answer 3

well techincally I did work but none of the answers matched mine

Answer 4

f(-3) = 2(-3) + 5

Answer 5

f(-3) = -6 + 5 = -1

Answer 6

did I screw up?

Answer 7

@Hero ?

Answer 8

you there dude?

Answer 9

Looks right so far, but ...

Answer 10

You should calculate f(g(x)) first, then calculate f(g(-3)).

Answer 11

oh. uhm how do I do that? thats the only thing that confuses me

Answer 12

I'll get you started:
f(x) = 2x + 5

1. Replace x with g(x)
f(g(x)) = 2(g(x)) + 5

2. Replace g(x) with x - 7
= 2(x - 7) + 5

3. Simplify the expression

Answer 13

hmm... 2x -14 +5?

Answer 14

So f(g(x)) = 2x - 14 + 5, but that can also be further reduced, right?

Answer 15

I think so

Answer 16

Because -14 + 5 = -9 so

f(g(x)) = 2x - 9

Now calculate f(g(-3))

Answer 17

hmm. so we would add 14 to both the 5 and the -14?

Answer 18

oh sorry. lol late comment there

Answer 19

@FrostFlare23 waiting on you ...

Answer 20

alright

Answer 21

so we would then divide 2 to both sides to isolate the X in order to get
x = 4.5?

Answer 22

No, you just simply evaluate f(g(x)) at x = -3

f(g(x)) = 2x - 9
f(g(-3)) = 2(-3) - 9

Answer 23

oh!

Answer 24

alright

Answer 25

so basically it would become: 2(-3) which equals -6. then we subtract -6 from 9 to get -15?

Answer 26

Correct.

Answer 27

ok so I was right I just ha the wrong way of doing it the first time thank you!

Answer 28

Both ways of doing it are correct. It's just better practice to write f(g(x)) as a single expression then evaluate it once.

Answer 29

alright thank you kind sir!

Answer 30

The problem with doing it the way is, if someone asked you what f(g(x)) is, you wouldn't be able to tell them.

Answer 31

oh ok