Question

If f(x) varies directly with x and f(x) = 24 when x = –4, then what is f(x) when x = 12?

Answer 1

Says he's offline :(

Answer 2

@jim_thompson5910 @jigglypuff314 @zepdrix plz help!!

Answer 3

Hey Michelle :)

Hmm so where we stuck?

Answer 4

Everywhere :(

Answer 5

i dont understand the problem, or i would have helped

Answer 6

If f(x) and x vary `directly`, that means that they're directly equal to one another, but vary by some constant. We usually call it k.

So we would write a direct relationship like:\[\Large\rm f(x)=k x\]

Answer 7

The first set of information they give you,
you want to use to solve for k.

Answer 8

x=-4
f(x)=24

plug those values in.
Then solve for k.
What do you get? :)

Answer 9

Comeon miss chelle! you can do this step! :U
plug em in,\[\Large\rm f(x)=k x\]\[\Large\rm 24=k (-4)\]Solve for k.

Answer 10

Is it -6?

Answer 11

Good good good.
So we'll plug that k value back into our general formula:\[\Large\rm f(x)=k x\]\[\Large\rm f(x)=-6x\]

Answer 12

Now we use the new information to solve for f(x).

x=12
f(x)=?

Answer 13

Is it -2?

Answer 14

We're not plugging 12 in here,\[\Large\rm \color{red}{12}=-6x\]We're plugging it in here,\[\Large\rm f(x)=-6\color{orchid}{x}\]

Answer 15

-48?

Answer 16

-6 times 12? :o
Hmm that doesn't sound right :c

Answer 17

-72