Logs are hell!

Take the log of both sides, simplify (log(xy) = log x + log y, log10=1 etc) and you get your answer. That's your standard exponential formula except you'll come across it as Ae^(kt) in things like radioactivity, so you use natural/Napier logs instead of log to the base 10.

"spoiler" :p

Taking log of both sides gives: (and calling z(0) = y to simplify things for me!)
log z = log (y*10^(-kt))

Simplifying by log(xy) = log(x) + log(y) gives:
log z = log y + log(10^-kt)

Simplifying using log(x^n) = nlogx gives:
log z = log y + (-kt)log(10)

Now, log(10) = 1 and thus;
log z = log y - kt (as required)

Now, where's my 50p :p
 
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It was the LogAB = LogA + logB rule I forgot.

Solution:

0504071653eo8.jpg


Thanks everyone.
 
Dave said:
Take the log of both sides, simplify (log(xy) = logx + log y, log10=1 etc) and you get your answer. That's your standard exponential formula except you'll come across it as Ae^(kt) in things like radioactivity, so you use natural/Napier logs instead of log to the base 10.

So how do you prove all that is true to a bunch of OcUk'ers? ;)
 
Dave said:
Take the log of both sides, simplify (log(xy) = log x + log y, log10=1 etc) and you get your answer. That's your standard exponential formula except you'll come across it as Ae^(kt) in things like radioactivity, so you use natural/Napier logs instead of log to the base 10.

"spoiler" :p

Taking log of both sides gives: (and calling z(0) = y to simplify things for me!)
log z = log (y*10^(-kt))

Simplifying by log(xy) = log(x) + log(y) gives:
log z = log y + log(10^-kt)

Simplifying using log(x^n) = nlogx gives:
log z = log y + (-kt)log(10)

Now, log(10) = 1 and thus;
log z = log y - kt (as required)

Now, where's my 50p :p

If I ever meet you, I will buy you a can of coke :D

Or is it 60p now? I forget.
 
Tommy B said:
If I ever meet you, I will buy you a can of coke :D

Or is it 60p now? I forget.

Bar of galaxy will do just as fine :p

If you're in Sheffield then we can meet up to come to some fiscal arrangement when I get back to university :p
 
Dave said:
Bar of galaxy will do just as fine :p

If you're in Sheffield then we can meet up to come to some fiscal arrangement when I get back to university :p

Really? I may end up there next year. My first two uni choices are Sheffield and Newcastle :)
 
I was late into this thread, silly me enjoying the sun all day...

Without knowing the content of the post, I'd have gone for:

Exlax_Plus_Stool_Softener_24Caplets_enlarge.jpg
 
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