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Math Help - Index Law

  1. #1
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    Index Law

    I got the answer x^2 + 49 from the question (x+7)^2.
    But then i was told the answer was x^2 +14x+49.

    could some explain the 14x pleas?
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  2. #2
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    e^(i*pi)'s Avatar
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    It [I assume you mean 14x not 40x] because (a+b)^2 \neq a^2+b^2

    You need to either memorise the result, use the binomial theorem or use the distributive property/FOIL.

    Using the distributive property (x+7)^2 = (x+7)(x+7) = x(x+7) + 7(x+7) = (x^2+7x) + (7x+49) = x^2+14x+49


    Memorising that (a+b)^2 = a^2+2ab+b^2 is a great timesaver in exams
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  3. #3
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    Thank you
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