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Logarithms help

Hi I just had a small question which i'm confused about if someone could help me please:

So on the disk it says
e to the power of lnk = k

why is this? I dont understand how e^lnk can be simplified to k?

Thank you!
Original post by assassinjeev22
Hi I just had a small question which i'm confused about if someone could help me please:

So on the disk it says
e to the power of lnk = k

why is this? I dont understand how e^lnk can be simplified to k?

Thank you!


'Ln' is the inverse function of 'e'.

So when f(x) = ln(x)
f^-1(x) = e^x and visa versa

This means lne^(x) = x and e^ln(x) = x
(edited 6 years ago)
Original post by Emmiassa
'Ln' is the inverse function of 'e'.

So when f(x) = ln(x)
f^-1(x) = e^x and visa versa

This means ln(e^x) = x and e^ln(x) = x


oh i see thank you!
Original post by assassinjeev22
oh i see thank you!


No problem :smile:
Reply 4
Original post by assassinjeev22
Hi I just had a small question which i'm confused about if someone could help me please:

So on the disk it says
e to the power of lnk = k

why is this? I dont understand how e^lnk can be simplified to k?

Thank you!

lnk=logek\ln k = \log_e k is the power that you need to raise e by to get k.

So elnke^{\ln k} is:

e to the power of (the power you need to raise e by to get k). If you think about for this a while you'll see that this must be equal to k.

In terms of functions, if f(x)=lnxf(x)=\ln x then f1(x)=exf^{-1}(x)=e^x so elnk=f1f(k)e^{\ln k} = f^{-1}f(k). If you put k through a function followed by its inverse then you'll get back to k.

Here's another explanation using log laws. And reading through the whole of that thread might be useful if you're still unsure.

EDIT : Too late!
Original post by Notnek
lnk=logek\ln k = \log_e k is the power that you need to raise e by to get k.

So elnke^{\ln k} is:

e to the power of (the power you need to raise e by to get k). If you think about for this a while you'll see that this must be equal to k.

In terms of functions, if f(x)=lnxf(x)=\ln x then f1(x)=exf^{-1}(x)=e^x so elnk=f1f(k)e^{\ln k} = f^{-1}f(k). If you put k through a function followed by its inverse then you'll get back to k.

Here's another explanation using log laws. And reading through the whole of that thread might be useful if you're still unsure.

EDIT : Too late!


Thank you!
Reply 6
Original post by Notnek
lnk=logek\ln k = \log_e k is the power that you need to raise e by to get k.

So elnke^{\ln k} is:

e to the power of (the power you need to raise e by to get k). If you think about for this a while you'll see that this must be equal to k.

In terms of functions, if f(x)=lnxf(x)=\ln x then f1(x)=exf^{-1}(x)=e^x so elnk=f1f(k)e^{\ln k} = f^{-1}f(k). If you put k through a function followed by its inverse then you'll get back to k.

Here's another explanation using log laws. And reading through the whole of that thread might be useful if you're still unsure.

EDIT : Too late!


Would lnklogek \ln k \equiv \log_e k be more appropriate than lnk=logek?\ln k = \log_e k?
Reply 7
Original post by Desmos
Would lnklogek \ln k \equiv \log_e k be more appropriate than lnk=logek?\ln k = \log_e k?

Technically maybe. I usually use \equiv when it is not clear whether something is an identity. Otherwise I use == and \equiv interchangeably for identities and I think that's fine.

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