Question

Let f(x) = x - 2 and g(x) = x2 - 7x - 9. Find f(g(-1)).


@mathmale

Answer 1

f(g(x)) = (x^2 - 7x - 9) - 2

Do the rest bby

Answer 2

well let's see, since its f(g(-1)), its hould be set up like ....lol nvm tHe_FiZiCx99 got it

Answer 3

if you want i could walk you through the rest

Answer 4

Why did my x obliterate itself off Earth.

Answer 5

basically plug in -1 in the g(x) equation. take the answer that u get and plug it into the f(x)

Answer 6

Okay, so -3.

Answer 7

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

Answer 8

well from the looks of it you need to factor

Answer 9

f(g(x)) = (x^2 - 7x - 9) - 2 was tHe_FiZiCx99's contribution and is correct.
You could either plug in x = -1 now or simplify his expression first and then plug in -1.

Answer 10

" (x^2 - 7x - 9) - 2"

Okay but f(x) = x - 2

So, if we have " (x^2 - 7x - 9) - 2" Where did the x go?

Answer 11

Just to be sure you're aware of this: f(g(x)) is a "composite function:"

f(g(x)) = (x^2 - 7x - 9) - 2

The idea here is that you write this GENERAL composition. Once you have this, you replace every instance of x with the given value -1.

Answer 12

f(g(x)) = (x^2 - 7x - 9) - 2 could be re-written as f(g(x)) = x^2 - 7x - 11. substituting -1 for x should produce the same final result as before.

Answer 13

Some hints: (-1)^2 = 1
7(-1) = -7

Answer 14

You asked:

"" (x^2 - 7x - 9) - 2"

Okay but f(x) = x - 2

So, if we have " (x^2 - 7x - 9) - 2" Where did the x go? "

Answer: In f(x) = x - 2, you replace 'x' on both sides of the equation with g(x), which is x^2 - 7x - 9.

Thus, f(x) = x - 2 becomes

f(g(x)) = [x^2 - 7x - 9] - 2,

and this reduces to

f(g(x)) = x^2 - 7x - 11.

Lastly, replace every instance of x by (-1).

Answer 15

This is all so confusing. Could you explain it from stage one, like Functions 101. I know what you're saying but I don't understand why.

Answer 16

"f(g(x)) = (x^2 - 7x - 9) - 2 could be re-written as f(g(x)) = x^2 - 7x - 11. "

How can it be rewritten as -11 at the end? Where did that come from? Did we take it out of the parenthesis?

Also, ho would we even solve it once we have f(g(x)) = x^2 - 7x - 11

And I'm still lost as to what happened to my lil x.

Answer 17

Omg Comp ♥ lmfaooooo

Answer 18

@compassionate so did you plug in -1 for g(x)?

Answer 19

No. What do you mean?

Answer 20

Stop trolling, moderators have more important things to do besides appease you. -.-

Answer 21

You tell 'em Sham <3

Answer 22

so basically the question is asking you to find what the output is when you plug -1 in for g(x) and take that output and plug that in for x in f(x)

Answer 23

Righto, but I have f(g(x)) = x^2 - 7x - 11

How would I even solve that?

Answer 24

hey comp can you post some nice math riddles after this question

Answer 25

okay do my way first it will make sense to you.

Answer 26

I don't understand your first way.

Answer 27

hmm okay so plug in -1 in for g(x) what do u get?

Answer 28

g(x) = x2 - 7x - 9
g(x) = -1 + 7 - 9
g(x) = -3

Answer 29

is that x^2 if so a negative * negative is a positive right? so do u think ur answer is right?

Answer 30

-2

Answer 31

Yeah, I thought it would be positive, but my calculator said -1. Such lies. I feel attacked.

Answer 32

show me how u got there

Answer 33

haha yea for your calc u need to make sure u have parentheses.

Answer 34

x2 - 7x - 9
-1^2 -7(-1) - 9
1 + 7 - 9
-1

DERP!

Answer 35

good job! so now plug in -1 in f(x) and tell me what u get

Answer 36

-3

Answer 37

show me ur work :)

Answer 38

f(x) = x - 2

So... -1 - 2

Answer 39

yup! good job! thats ur asnwer:)

Answer 40

That would I originally concluded, but I redid it and got 21 so I wasn't sure. I appreciate your time, tejasvir.

You'd make a great Ambassador.

Answer 41

np:) haha thanks:P