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Math Help - find the product

  1. #1
    Newbie
    Joined
    Mar 2010
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    20

    find the product

    (x+1)(x-1) ; (2x+5y)(2x-5y) ; (x-9)(x+9) ; (5x-8y)(5x+8y) ;
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  2. #2
    Senior Member
    Joined
    Feb 2010
    Posts
    422
    (x+1)(x-1) = x(x-1) + 1(x-1) = x^2 -x + x - 1 = x^2 - 1
    (2x+5y)(2x-5y) = 2x(2x-5y) + 5y(2x - 5y) = 4x^2 - 10xy +10xy -25y^2

    ...you can go on. Notice the pattern?

    (a+b)(a-b) = a(a-b) + b(a-b) = a^2 -ab + ba - b^2 = a^2 - b^2
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