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Homework Help: Tricky question involving laws of indices

  1. Jan 2, 2009 #1
    1. Find value of x if:

    4x-1 = 1/32



    3. I know that both 4 and 1/32 can be expressed as powers of 2 so (22)x-1 = 2-5

    Heres what im not quite sure about
    Im just assuming that I multiply that -1 by the power inside the brackets but im not sure if thats right. Anyhow heres what i got
    22x-2 = 2-5

    I then eliminated the 2s so Im left with 2x-2 = -5.

    doing that in my head I get x = -3/2

    plugging that into the equation doesn't work unfortunately.
     
  2. jcsd
  3. Jan 2, 2009 #2

    HallsofIvy

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    Science Advisor

    It looks to me like it works. If x= -3/2 then 2x-2= -3-2= -5 so the left side is 2-5= 1/32, exactly like the right side.
     
  4. Jan 2, 2009 #3
    If you were checking in the original equation...
    [tex]4^{-\frac{3}{2}-1}=
    4^{-\frac{5}{2}}=
    (2^{2})^{-\frac{5}{2}}=
    2^{-5}=
    \frac{1}{32}[/tex]


    01
     
  5. Jan 3, 2009 #4
    Ah yeah I didn't see that it came out to 2^-5 in the end thanks. Was my method right? I think they take marks off u for taking roundabout methods.
     
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