1. Logorithms- help understanding knowledge

We were given raw data on temperature of coffee cooling over time

What I don't get is why they say investigate power model in the form y=ax^n by to plotting this raw data and log x vs log y?

What is log x is it log to base 10 or lnx? What does it mean?- its is the rate of change of the x variable or something?
Same for Log y?

Then in y=Ae^kx why do we plot x vs log y?

Im sure there is a reason like one is the opposite of the other.. :S

Im just confused? anyone help me?
plz thanks

2. Re: Logorithms- help understanding knowledge

Originally Posted by Mathshelp246
We were given raw data on temperature of coffee cooling over time

What I don't get is why they say investigate power model in the form y=ax^n by to plotting this raw data and log x vs log y?

What is log x is it log to base 10 or lnx? What does it mean?- its is the rate of change of the x variable or something?
Same for Log y?

Then in y=Ae^kx why do we plot x vs log y?

Im sure there is a reason like one is the opposite of the other.. :S

Im just confused? anyone help me?
plz thanks
you can take either log or ln, with the condition that you keep the same base for all your operations,

another point - I assume they suggest you to take the log of x and y in order to find the coeficient k, that determines the cooling over time,

hope this helps,

dokrbb

3. Re: Logorithms- help understanding knowledge

Thanks for the reply , Im just unsure how plotting log x vs log y would give the coefficient "k", let alone what log x and log y are?

4. Re: Logorithms- help understanding knowledge

When you say you don't know "what log x and log y are" are you saying you have never studied logarithms? If you haven't I have no idea why you would be given this problem. If you have then you should know that log(y)= log(Axn)= nlog(x)+ log(A). That is, the graph of "log(y)" against "log(x)" is a straight line.

5. Re: Logorithms- help understanding knowledge

I only know how to solve log equations but these log graphs are new to me or ( we have only touched on them very little during class)- either way - Im new to log graphs :S. Ive researched a bit an found that log x vs log y is a straight line as you said before. The thing I don't get is why plot log graphs? i.e. log x vs log y? is it showing the same data as in the normal x vs y, but just instead as a straight line? or does plotting log x vs log y have something to do with reducing the scale size?, because the normal data is a curving line from the top left of the y axis to the bottom right of the x axis - like an exponential decay.