Question

Tell me where I messed up ?

f(x)=-4x-1 when f(x) is -2

f(-2)=-4(-2)-1
f=-4(-2)-1+2
f=8-1+2
f=7+2
f=9

But -9 is an answer . :/

Answer 1

Uh, you messed up on the third step

Answer 2

Where did that +2 come from?

Answer 3

the f(-2) is just like saying "y, when x=-2"

Answer 4

But ..

Answer 5

I dont understand .

Answer 6

f(x)=-4x-1 when f(x) is -2

f(-2)=-4(-2)-1
f(-2)=8-1
f(-2)=7

Answer 7

So you dont move the -2 on the left side ? :/

Answer 8

\[f(-2)=-4(-2)-1\]\[f(-2)=8-1\]\[f=7\]

Answer 9

There is no -2 on the left

Answer 10

F(-2) is what someone else said .

Answer 11

It's just saying that you plug in -2 where ever there is an x

Answer 12

Yeah & I thought you had to isolate F .

Answer 13

f(x) means the function of x
f(-2) means the function when x is -2

bascially f(anything) is like saying 'y'
the only reason it is written as f(-2) is so that we know that they want "the value of the FUCNTION when X is" -2

Answer 14

Noooooo......
f(x)=-4x-1 when f(x) is -2 means

-2=-4x-1

Answer 15

f(x) is f sub x .

Answer 16

@DebbieG no, you must be thinking of substitution or something

Answer 17

It says WHEN F(X) IS -2.

That isn't when x=2, it's when f(x)=-2

Answer 18

oh wait....debbie's right

they want the value of x when f(x) is -2

\[f(x)=-4x-1\]\[-2=-4x-1\]

Answer 19

Wait.. darn it

Answer 20

@Sceenie , is 1/4 by chance an answer?

Answer 21

@Luigi0210 it says when f(x) is -2, not f(-2)

Answer 22

<--- what she said. :P

Answer 23

Hey, you made the same mistake yummy xD

Answer 24

No , It's not . The answers are
-9
-7
-10
7

Answer 25

yea i know, i think we got caught up with the fact that she completely misunderstood f(x)

Answer 26

Well, that's interesting. Is that the whole question up above? Exactly as you have it?

Answer 27

*smack* I hate math . xD

Answer 28

Well if we did need to plug in -2 for x, the answer would of been -7

Answer 29

Which is a choice

Answer 30

DON'T HATE ON THE MATH! :)

Answer 31

If f(x) = −4x − 1, find f(−2).

Answer 32

Yes then what we explained is correct and the answer is -7

Answer 33

ah HA! that's different than what you posted above! :) lol

Answer 34

Hah, @Luigi0210 we were right! :D

Answer 35

Yay!

Answer 36

(And has a very different meaning. :)

Answer 37

^yes

Answer 38

Next time write it word for word

Answer 39

*cries internally* I thought it was substitution .

Answer 40

Don't re-word or anything

Answer 41

you are substituting....substituting -2 for x

Answer 42

I didnt reword , i typed what I had written on my paper.

Answer 43

's ok.... it's instructive and useful to see what a huge difference that slight change in the language makes! :) And we got to the bottom of it, so all is well. :)

Answer 44

Just, whoever taught you functions didnt do a great job at explaining the concept of f(x)

Answer 45

^

Answer 46

< Wasnt taught how to do it .

Answer 47

did you skip a level of math?

Answer 48

So is it 7 ?

Answer 49

i mean Seven lol sorry

Answer 50

DONT YELL .

Answer 51

But
\(\Large \text{f(x)=-4x-1 when f(x) is -2}\)
is different from
\(\Large \text {If f(x) = −4x − 1, find f(−2).}\)

Do you see the difference?

Answer 52

Who's yelling?

Answer 53

Yes & Thank you , Debbie .c:

Answer 54

Anyway, we're all grown ups here (I'd like to think)
the situation is handeled, just make sure next time you type exactly what the question asks because now you see how the slightest difference changes the whole question.

Answer 55

You're welcome. :) I always say, "math is a precise science!" :) Little differences make a big difference sometimes, lol. :)