Question

If f(x) varies directly with x2, and f(x) = 72 when x = 6, find the value of f(3)

Help?

Answer 1

f(3) means when x = 3

Answer 2

72 = 2x

Answer 3

Nope

Answer 4

Would it be 18

Answer 5

@adamaero

Answer 6

for x = 3
or x = 6?
but actually I think I read the problem too fast, I lead you down the wrong path...
let me check...

Answer 7

x=6. I think.

Answer 8

I'm just generally confused about this entire thing lol.

Answer 9

are you sure it's not x^2
?

Answer 10

Oh, sh** lol. I forgot to put the little ^. Yes, it's x^2. Sorry about that.. haha

Answer 11

lol, you can't swear on here anyways
flutter that feather

Answer 12

I know haha, I've tried it before.

Answer 13

wio's already on the way answering it for you:

http://openstudy.com/study#/updates/54877db4e4b0c0f1a1527fc0

Answer 14

here is someone else answering it for you:

http://openstudy.com/study#/updates/54877e6be4b0c0f1a1528099

Answer 15

Oh. Okay. Thanks so much lol

Answer 16

@Chelleyhi are you there?

Answer 17

\[f(x)=kx^2 \]
this is the first translation you should get

Answer 18

now we can find the constant k given the second sentence
the second sentence says we have f(x)=72 when x=6
so we have 72=k(6)^2

Answer 19

solving that for k gives us what?

Answer 20

18?

Answer 21

72/36= is that 18

Answer 22

let me think
72/36=2

Answer 23

isn't it?

Answer 24

since 36+36=72
there are 2(36)=72
so 2=72/36

Answer 25

\[f(x)=kx^2 \\ \text{ so k is 2} \\ f(x)=2x^2 \]

Answer 26

now just plug in 3 to find f(3)

Answer 27

f(3)=2(3)^2

Answer 28

oh do you mean f(3)=18
if so yes

Answer 29

since 2*3^2=2*9=18

Answer 30

Thank you for your help, I did a bunch of googling and finally figured out how to do it.

Answer 31

Good job you! :)