# Exponential Growth for Pre-Calculus

1. May 24, 2009

### PrecalcStuden

Hi everyone.

My final is coming up for Precalc, and I'm studying my butt off.

I was really needing help with this Exponential Growth Equation to find variable t.

8.0e^(.033t) = 59.8e^(.001t)

(8 times e to the .033t equals 59.8 times e to the .001t)

I would greatly appreciate this because I'm stressing out for my finals. I have always been bad at this stuff

2. May 24, 2009

### CRGreathouse

Just take the logarithm of both sides and it's easy to solve.

3. May 24, 2009

### PrecalcStuden

I know it sounds like I'm asking you to do it for me, but I really don't know where to begin. I'm confuzed because of the coefficients, because i can just natural log both sides if there weren't any.

If you can please guide me good sir, I KNOW I can do the rest of this subchapter by myself. Thanks a bunch

4. May 24, 2009

### PrecalcStuden

I know it's simple for you, but I swear it's so complicated for me. Please, this would really help me my kind sir

5. May 24, 2009

### Integral

Staff Emeritus
What do you know about logs?

Review the basic laws, look especially at logs and multiplication. Also study the relationship between e and ln.

6. May 24, 2009

### PrecalcStuden

I know about logs my good sir. It's just this one problem tripping me up. I just really need someone to show me how its done, and your help will defaintely be appreciated. Should i make one side equal zero? i just dont know,

7. May 24, 2009

### PrecalcStuden

will someone please help, this is the last problem i need and im done with this sub chater

8. May 24, 2009

### PrecalcStuden

Please, I really need help with this.

I have to solve for t here.

8.0e^( .033t ) = 59.8e^ (.001t)

Please, i just really need you to show me how this is done.

9. May 24, 2009

### Staff: Mentor

exey = ex+y

10. May 24, 2009

### PrecalcStuden

I know that, but this is a weird one with weird coefficients. Please just walk me through this. gosh, im stressing out already

11. May 24, 2009

### yeongil

So CRGreathouse is suggesting to do this:

$$8.0e^{.033t} = 59.8e^{.001t}$$

$$\ln{(8.0e^{.033t})} = \ln{(59.8e^{.001t})}$$

Tell us what to do next.

01

12. May 24, 2009

### PrecalcStuden

so will it then turn into

ln 8.0 (.033t) = ln 59.8 (.001t)

Please ive been wait all day just to solve this one dang problem.

13. May 24, 2009

### Integral

Staff Emeritus
No, You need to use the laws for logs and multiplication.

14. May 24, 2009

### PrecalcStuden

integral, i beg of you. i just really need someone to help me with this mroe in depth. i've been waiting all day, i would really appreciate it integral. please

15. May 24, 2009

### PrecalcStuden

would someone pklease help me. Im begign you guys. I need help with this. geeze

16. May 24, 2009

### PrecalcStuden

17. May 24, 2009

### PrecalcStuden

im begging yiou guys

18. May 24, 2009

### Integral

Staff Emeritus
We need to see some effort on your part. Show me that you have even tried to apply the hints you have been given.

Your problem is of the form:

$$A e^x = B e^y$$
So taking the ln:
$$ln(A e^x) = ln (B e^y)$$

since ln(a * b ) = lna + lnb
$$lnA + ln(e^x) = lnB + ln(e^y)$$

Can you finish?

19. May 24, 2009

### PrecalcStuden

Integral, thank you kind sir.

Let's see here.

Yes sir.

Looks like it will be

ln 80 + .033t = ln 59.8 + .001t

From there

ln 80 - ln 59.8 = .001t - .033t

ln 80 - ln 59.8 = -.032
then divide and use a calculatro

something isnt adding up quite right sir, im getting a negattive numbe[/I]

wait, edit, it's ln 8 not 80. Thank you integral YOU ARE SO NICE. thank u so much.

Last edited: May 24, 2009
20. May 24, 2009

### HallsofIvy

Staff Emeritus
You have been helped repeatedly. How about doing something yourself?\
You have been told exactly what to do. Why do you keep whining "do it for me! Do it for me!"?