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Log Q higher level maths

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  • 19-05-2009 3:11pm
    #1
    likely_lass
    Closed Accounts Posts: 335 ✭✭


    was going over logs there and this question has my brain destroyed- cant ask the teacher because ive already left school

    the Q says show that logaB = 1/logbA
    if x>0 and x not equal to 1 show that,
    1/log2X + 1/log3X + 1/ log5X = 1/log30X



    the solution says

    logaB = logbB/logbA = 1/logbA
    ^This bit is whats really confusing me


    Then,
    1/log2X + 1/log3X + 1/log5X
    =logX2+logX3+logX5
    =logX(2x3x5)
    =logX30
    = 1/log30X



    IF ANYONE CAN HELP IT WOULD BE SOOOOOOO APPRECIATED


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    #2
    PurpleFistMixer
    Registered Users Posts: 5,851 ✭✭✭PurpleFistMixer


    likely_lass wrote: »
    logaB = logbB/logbA = 1/logbA
    ^This bit is whats really confusing me
    Looks like they're using the change of base rule here. Then logbB is just equal to 1 (b to the power of what is b?), so it gives 1/logbA.


  • Options
    #3
    likely_lass
    Closed Accounts Posts: 335 ✭✭likely_lass


    PurpleFistMixer wrote: »
    Looks like they're using the change of base rule here. Then logbB is just equal to 1 (b to the power of what is b?), so it gives 1/logbA.

    thanks i see it now, dont know how i didnt before, must need some air


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