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How do I solve for x to two decimal places in the following?

  • 26-11-2012 5:40am
    #1
    xerces
    Registered Users, Registered Users 2 Posts: 805 ✭✭✭


    Hi,

    I'm looking for some help with solving for x to two decimal places in the following:

    (1+3x)^5=6


Comments

  • #2
    Pherekydes
    Registered Users, Registered Users 2 Posts: 16,202 ✭✭✭✭Pherekydes


    Use logs.


  • #3
    MathsManiac
    Registered Users, Registered Users 2 Posts: 1,595 ✭✭✭MathsManiac


    ...or take the fifth root of both sides. (Your calculator should be able to work out the fifth root of 6.)


  • #4
    xerces
    Registered Users, Registered Users 2 Posts: 805 ✭✭✭xerces


    MathsManiac wrote: »
    ...or take the fifth root of both sides. (Your calculator should be able to work out the fifth root of 6.)

    Ah yes, how silly of me. So going that route, it'll be:

    (1+3x)^5=6
    1+3x=1.43 (done by calc)
    3x=0.43
    x=0.14

    Thanks for your help.


  • #5
    MathsManiac
    Registered Users, Registered Users 2 Posts: 1,595 ✭✭✭MathsManiac


    By the way, I would recommend not to do the rounding until the end. It doesn't make any difference in this case, but if you rounded your fifth root to two decimal places and then you later did certain kinds of calculation, the error arising from early rounding could get magnified in the answer.

    So, whatever way you record on the page is one thing, but I'd hold the full value of the root on the calculator while doing the remaining calculations.


  • #6
    Yakuza
    Registered Users, Registered Users 2 Posts: 5,141 ✭✭✭Yakuza


    MathsManiac wrote: »
    By the way, I would recommend not to do the rounding until the end. It doesn't make any difference in this case, but if you rounded your fifth root to two decimal places and then you later did certain kinds of calculation, the error arising from early rounding could get magnified in the answer.

    So, whatever way you record on the page is one thing, but I'd hold the full value of the root on the calculator while doing the remaining calculations.

    +1

    (or in this case, +1.00 :))


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  • #7
    xerces
    Registered Users, Registered Users 2 Posts: 805 ✭✭✭xerces


    MathsManiac wrote: »
    By the way, I would recommend not to do the rounding until the end. It doesn't make any difference in this case, but if you rounded your fifth root to two decimal places and then you later did certain kinds of calculation, the error arising from early rounding could get magnified in the answer.

    So, whatever way you record on the page is one thing, but I'd hold the full value of the root on the calculator while doing the remaining calculations.

    I see what you're saying, much thanks.


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