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Homework Help: Addition Of Exponents

  1. Feb 25, 2010 #1
    So I just got back from my math class, we were going over exponents. Right before we left he gave us a problem and we turned it in, I was just wondering if I got it right.

    Simplify:
    (54-3y)3 * (5y-2)2

    I got:
    512-9y3 * 5y2-4

    5-9y3+y2+8

    I applied the powers to the parenthesis, then added the two exponents. The addition of the exponents is here:
    http://www.wolframalpha.com/input/?i=%2812-9y^3%29+%2B+%28y^2+-+4%29

    However when I just pop the original problem into wolfram alpha I get:
    http://www.wolframalpha.com/input/?i=%28%285^%284-3y%29%29^3%29+*+%28%285^%28y-2%29%29^2%29
    58-7y

    So I guess I have two questions. First is my answer right? Second how did Wolfram come up with that answer?
     
  2. jcsd
  3. Feb 25, 2010 #2
    You are applying the exponentiation rules incorrectly in your first step - perhaps you want to review it. When you bring down the 3, you multiply it to the (4-3y) to get (12-9y) instead of taking powers. Do the same for the other term. Then you can reduce the exponents.

    See rules 3 here: http://mathworld.wolfram.com/ExponentLaws.html
     
  4. Feb 25, 2010 #3
    Thanks. Stupid mistake, always the stupid mistakes.
     
  5. Feb 25, 2010 #4
    That's fine - when you make mistakes you go back and look at the definitions, problems, and learn a lot that way. Cheers
     
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