# Math Help - Direct variation help

1. ## 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

3. 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.

4. Originally Posted by ssppsabres

-Dan

6. 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

7. y=1.5?

8. Originally Posted by ssppsabres
y=1.5?
how did you get that from the equation 3x - 4y = 9 ?

9. y=3?

10. 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 $y = kx$ ?

11. No, so therefore it is not a DV and has no constant?

12. So no its not?

Question #1 asked "Do the following equations represent direct variations? If so, find the constant of variation
1. 3x-4y=9"
and when asked to post your solution, you posted, in three separate posts,
"y=1.5? "

"y=3? "

"So no its not?"

The first two make no sense because you were not asked to find a value of y. The last makes no sense because it is not a complete sentence- "so no its not" what?

Since the questions asks, first whether or not the relation given is a "direct variation", you should start by stating what a direct variatio is and then show how the given relation does or does not satisfy that. If it is a direct variation, then you should give the constant of variation, which is NOT "y".