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    i completely forgot how to work these out =|
    anyone help me out pleaseee

    i need to work out k, ive forgotten how to use ln...

    80 = 40e^21k

    (e is raised to the power of 21k)
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    as we aren't allowed (meant) to give worked solutions on here... heres a hint...

    natural logs...
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    i tried doing this:

    ln2 / ln21 = k
    but that didnt work out

    then i tried doing

    ln2 /ln21 = lnk ...but that doesnt make sense...

    so not really sure where im going with this

    i got the ln 2, from doing 80/40
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    (Original post by disisme)
    i tried doing this:

    ln2 / ln21 = k
    but that didnt work out

    then i tried doing

    ln2 /ln21 = lnk ...but that doesnt make sense...

    so not really sure where im going with this

    i got the ln 2, from doing 80/40

    Where did u get the ln21 from? Remember :  ln(e^a)=a as ln and e are inverse functions of each other.
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    (Original post by disisme)
    i tried doing this:

    ln2 / ln21 = k
    but that didnt work out

    then i tried doing

    ln2 /ln21 = lnk ...but that doesnt make sense...

    so not really sure where im going with this

    i got the ln 2, from doing 80/40
    Don't forget that the natural log cancels with the exponential so its actually 21k = ln2.
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    (Original post by didgeridoo12uk)
    as we aren't allowed (meant) to give worked solutions on here... heres a hint...

    natural logs...

    okay so i found this written in my notebook, i did it last year..but cannot remember what i did/how to do it!!!

    i wrote..

    lne^21k = ln2
    21lnk=ln2
    21k=ln2

    which gives me the right answer....but how/why did i get rid of the ln from the 21k???!!!
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    (Original post by JBKProductions)
    Don't forget that the natural log cancels with the exponential so its actually 21k = ln2.

    ooohhh okay thanks!! that was my next post lol..i didnt realise that!
    cool tinnnngs
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    (Original post by disisme)
    okay so i found this written in my notebook, i did it last year..but cannot remember what i did/how to do it!!!

    i wrote..

    lne^21k = ln2
    21lnk=ln2
    21k=ln2

    which gives me the right answer....but how/why did i get rid of the ln from the 21k???!!!
    that line is wrong!

    basically you need to make use of the two rules...

    ln(a^b) = b ln(a)

    ln(e) = 1

    or

     ln(e^x) = x

    depending on how you want to think about it
 
 
 
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