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Homework Help: I can't finid the answer

  1. Mar 5, 2010 #1
    Hi

    i can't finid the answer

    1 - If a1 = 1 and a5 = 100 then r = ?
    2 - If a1 = 324 and a9 = 4 then r = ?

    "" my answer ""

    1 - a5 = a1r^n-1
    = 1 (r)^4 = 100
    r = (100)^1/4
    = 25 but the teacher said mistake .

    2 - a9 = a1r^n-1
    = 324 (r)^8 = 4
    = (4)^1/8 = 0.5 but also the teacher said mistake .

    ------------


    help me
     
  2. jcsd
  3. Mar 5, 2010 #2

    Cyosis

    User Avatar
    Homework Helper

    Raising something to the power of 1/4 is not the same as dividing by 4 which is what you have done from the looks of it. If you typed it like that into your calculator the calculator would think that 100^1/4=(100^1)/4. Try to type 100^(1/4).
     
  4. Mar 5, 2010 #3
    thanks a lot
     
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