Understanding Logarithmic Identities in Differential Equations

In summary, The conversation includes a discussion about differential equations and log identities. The equation 1/8 lny = t + c is simplified to y = ce^8t, using the identity ln(y^{{1}\over{8}}) = 1/8 ln(y). The participants also joke about tattooing logarithmic identities and burning them behind their retinae, and mention the sadistic nature of exams.
  • #1
HeLiXe
440
1
This is related to differential equations, but I think my question has more to do with log identities than DE.

I keep seeing equations like

1/8 lny = t + c

simplified to get the solution

y = ce^8t

but I am unsure of the identity being used to get 1/8 into the exponent as 8. I already understand how everything else is simplified, just not this part. Thanks!
 
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  • #2
Just multiply both sides by 8 and exponentiate both sides.

The other way to see this would be that [itex]1/8 ln(y) = ln(y^{{1}\over{8}})[/itex]
 
  • #3
*facepalm* Thanks penguwino LOL
 
  • #4
That'll be $5
 
  • #5
I'll give you $25 :tongue2:

I kept switching it over the entire semester and never understood why I was doing that loll. This is what happens when the "simple steps" are skipped in math -_-
 
  • #6
Tattoo the logarithmic identities to your forearm. It's far more useful then some rose or star
 
  • #7
^ But then to avoid being suspected of cheating, you'd have to wear full-sleeve shirts during your exams. And that sucks when your exams are seated outside during a heatwave :(
 
  • #8
Pengwuino said:
Tattoo the logarithmic identities to your forearm. It's far more useful then some rose or star
I'll see if I can have them burned on my retina :D
Dr. Seafood said:
And that sucks when your exams are seated outside during a heatwave :(
That is so sadistic! -_- Who would ever do such a thing to an innocent student?
 
  • #9
HeLiXe said:
I'll see if I can have them burned on my retina :D

Try to burn them behind your retinas.
That works even better! ;)


HeLiXe said:
That is so sadistic! -_- Who would ever do such a thing to an innocent student?

Oh, standard trick to flush out not-so-innocent students.
 
  • #10
I like Serena said:
Try to burn them behind your retinas.
That works even better! ;)

If there was something behind my retinae it would work better :tongue2:
 

What is a logarithmic identity?

A logarithmic identity is an equation that relates two logarithmic expressions, and it remains true regardless of the values of the variables involved.

How do I simplify logarithmic identities?

To simplify a logarithmic identity, you can use properties of logarithms, such as the power rule, product rule, quotient rule, and change of base rule. These properties allow you to rewrite the expression in a simpler form.

Why are logarithmic identities useful?

Logarithmic identities are useful in solving exponential and logarithmic equations, as well as in graphing logarithmic functions. They also have applications in fields such as physics, chemistry, and economics.

What are some common logarithmic identities?

Some common logarithmic identities include log(a*b) = log(a) + log(b) (product rule), log(a/b) = log(a) - log(b) (quotient rule), and log(a^b) = b*log(a) (power rule). There are also identities for changing the base of a logarithm and for simplifying logarithms of square roots and exponents.

How can I remember all the logarithmic identities?

It can be helpful to practice using the various properties of logarithms and to memorize the most common identities. You can also create a cheat sheet or use mnemonic devices to remember them. With practice, you will become more familiar with the identities and their applications.

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