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Properties of exponents and logs problem

  1. Sep 19, 2009 #1
    Find B when given: Y = log2B and 2y+4 + 4y+3 = 224

    I could use some help figuring out the process to this. Thanks
     
  2. jcsd
  3. Sep 19, 2009 #2

    rock.freak667

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    Homework Helper

    Re: Logs

    the log of a number is the power to which the base is raised to give that number

    so if z=ab then b=logaz
     
  4. Sep 20, 2009 #3
    Re: Logs

    I'm still having trouble. 2y=z and y+4=log2Z and y+3=log4R? What do I do with this? Could you help me solve it please I am kind of lost.

    I get Z + R = 224 and B = 2Y Now what?
     
  5. Sep 20, 2009 #4
    Re: Logs

    You need to remember some properties of exponents:

    xa+b = xa·xb
    xab = (xa)b

    Also, it can help to rewrite 4 as 22.

    When you can rewrite the equation with 2y, replace them with B and then solve for B.
     
  6. Sep 20, 2009 #5
    Re: Logs

    Ok so I got a funky answer.

    2y24+22y26=224
    B=2y So,
    16B+64B2=224
    4B2+B=14

    I ended up with B=-2 but that doesn't make sense with -2=2y
     
  7. Sep 20, 2009 #6
    Re: Logs

    That's only one (extraneous) root of the quadratic equation you got. The other one is the correct answer.
     
  8. Sep 20, 2009 #7
    Re: Logs

    Ah 7/4 thanks!
     
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