# Thread: Having trouble with this one.

1. ## Having trouble with this one.

Guys,

I am new here so please forgive my ignorance.

Need help with the following:
Y = A*ln(B*ec*x - D*Y)

Where A, B, C, D are constants. I would like to determine the if there is a 20% change in "x" what is the corresponding change/impact on "Y"?

Thanks.

2. ## Re: Having trouble with this one.

Originally Posted by Joesph
Guys,

I am new here so please forgive my ignorance.

Need help with the following:
Y = A*ln(B*ec*x - D*Y)

Where A, B, C, D are constants. I would like to determine the if there is a 20% change in "x" what is the corresponding change/impact on "Y"?

Thanks.
Is it a 20% increase or decrease in x?

3. ## Re: Having trouble with this one.

A 20% increase in "x"

4. ## Re: Having trouble with this one.

If you increase x by 20%, you end up with x + 0.2x = 1.2x, so replace x with 1.2x and see what effect this has.

5. ## Re: Having trouble with this one.

Thanks for the quick replys, but that's the part I don't know how to solve.

6. ## Re: Having trouble with this one.

Show me what you've tried. Start by replacing x with 1.2x...

7. ## Re: Having trouble with this one.

I would need to solve for "Y" first. The problem is that I do not know how to do that since both the left and right sides contain "Y"
Y = A*ln(B*ec*x - D*Y)
if I simply put Y = A*ln(B*ec*1.2x - D*Y), I would still need a way to solve for "Y"

8. ## Re: Having trouble with this one.

Hello, Joesph!

$\text{I would need to solve for }y\text{ first.}$ . You can't!

$\text{We have: }\:y \;=\;A\ln(Be^{cx} - Dy)$

$\text{We have a }transcendental\text{ equation.}$
$y\text{ is both inside and outside of a log function.}$

$\text{It cannot be solved for }y.$