# Direct variation help

• Feb 8th 2011, 06:29 PM
ssppsabres
Direct variation help

Do the following equations represent direct variations? If so, find the constant of variation

1. 3x-4y=9
2. y=1/5y
3. 8x=4y

thanks
• Feb 8th 2011, 06:39 PM
ssppsabres
• Feb 8th 2011, 06:54 PM
skeeter
two variables, y and x, are in a direct variation if y and x can be written in the form y = kx , where k is any constant.
• Feb 8th 2011, 06:57 PM
topsquark
Quote:

Originally Posted by ssppsabres

-Dan
• Feb 8th 2011, 06:57 PM
ssppsabres
• Feb 8th 2011, 07:06 PM
topsquark
Look at the first equation. Solve it for y. Is this in the form y = kx? Use the same method for the other two. Post your solution for #1 (or either of the others) so we can see if you err at some point.

-Dan
• Feb 8th 2011, 07:15 PM
ssppsabres
y=1.5?
• Feb 8th 2011, 07:17 PM
skeeter
Quote:

Originally Posted by ssppsabres
y=1.5?

how did you get that from the equation 3x - 4y = 9 ?
• Feb 8th 2011, 07:20 PM
ssppsabres
y=3?
• Feb 8th 2011, 07:27 PM
skeeter
Quote:

Originally Posted by ssppsabres
y=3?

no. you are guessing.

$3x - 4y = 9$

$3x - 9 = 4y$

$\dfrac{3x}{4} - \dfrac{9}{4} = y$

or

$y = \dfrac{3x}{4} - \dfrac{9}{4}$

now ... is this equation in the form $y = kx$ ?
• Feb 8th 2011, 07:30 PM
ssppsabres
No, so therefore it is not a DV and has no constant?
• Feb 8th 2011, 08:33 PM
ssppsabres
So no its not?
• Feb 9th 2011, 04:32 AM
HallsofIvy