Math help please?

[ManBearPig]

how would i do:

3·8^x = 6.5e^4x

thanks

 

[TuxDave]

log (a^b) = b*log(a)

 

[BigJ]

http://www.mathwords.com/l/logarithm_rules.htm

 

[ManBearPig]

still dont get it

 

[chuckywang]

Originally posted by: Heen05
how would i do:

3·8^x = 6.5e^4x

thanks

Take the log of both sides. Doesn't matter which base.

 

[chuckywang]

Alright fine....

3*8^x = 6.5*e^(4x)

3/6.5 = (e^4/8)^x

See if that helps.

 

[ManBearPig]

sweet...thanks chucky, i appreciate it.

any idea how to do this? i cant figure it out anywhere...its pissing me off


effective annual yield = 6.3%:

What is the nominal annual interest rate? _______%

 

[ManBearPig]

bump

 

[chuckywang]

Did you understand my hints? Did you set up the equation correctly?

 

[TheoPetro]

you need to do your own homework. most people here dont mind given a hint or two or even showing you the steps to do it but were not going to do all of your homework for you.

 

[Paperdoc]

Clue: Chuck Wang got his algebra wrong! What he should have written is:

3/6.5 = [e^(4x)] / [8^x] (extra [ and ] just to make it very clear)

and that is NOT the same.

As others said, you need to use logarithm rules and take the logarithm of each side. Since one term is an e^(4x), taking Natural (base e) logarithms comes to mind. Eventually you will need a reference point to find the actual value of a natural logarithm of a number, and that will use a math-oriented calculator.

I suspect the whole reason you have this to deal with is that some person wanted you to learn how to use logarithms.

 

[us3rnotfound]

ln(3)+xln(8) = ln(6.5) + 4x
ln(3)-ln(6.5)=x(4-ln(8))
(ln(3)-ln(6.5))/(4-ln(8)) = x

 

[dullard]

0) Write your formula so that the rest of us know what you mean. USE PARENTHESES PEOPLE! I assume you meant to type this instead: 3*8^x = 6.5*e^(4*x). Those last parentheses are very important.

1) Open Excel.
2) Type a guess for x into any cell.
3) Rearrange the formula so that it equals zero like this: 3*8^x - 6.5*e^(4*x) = 0.
4) Type that rearranged formula into any other Excel cell. It will look like this (I guessed x=1): Excel beginning.
5) Go to the Excel Tool menu and click Solver. It isn't installed by default, but it is the single most powerful part of Excel by far. Get out your CD if it isn't there and install it. Tell the solver to adjust "x" until the formula is equal to zero. Like this.
6) Excel solved it for you. Answer.

7) This simple method would solve 99% of math questions asked on ATOT. Spread the word (no horrible MS Office pun intended).

Note: you can adjust the Excel settings to get a bit closer than 2.77*10^-7 for the formula if you wish, but "x" won't change in any significant way.

 

[Tiamat]

Goal seek or solver like dullard said for checking your analytical solution. Since you will not have excel at your disposal for the exam, just use it to check your answers.