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Math Help - simplifying out brackets.....

  1. #1
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    simplifying out brackets.....

    Hi...

    I presumed I was right in taking 3(a^2 + b^2) - a(b + 2a) +2b(a+3b) down to 3a^2 + 3b^2 - ab + 2a^2 + 2ba + 6b

    my friend just said he thinks im going about it in the wrong way??
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  2. #2
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    3(a^2 + b^2) - a(b + 2a) +2b(a+3b)
    =3a^2 + 3b^2 - ab -2a^2 + 2ab + 6b^2

    In your answer you put +2a^2 which is incorrect and is instead - 2a^2
    Be careful with your signs infront of brackets when you multiply.
    Hope it helpsx

    Regards,
    Amazed
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  3. #3
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    Quote Originally Posted by bobchiba View Post
    Hi...

    I presumed I was right in taking 3(a^2 + b^2) - a(b + 2a) +2b(a+3b) down to 3a^2 + 3b^2 - ab + 2a^2 + 2ba + 6b

    my friend just said he thinks im going about it in the wrong way??
    3(a^2 + b^2) - a(b + 2a) +2b(a+3b) = 3a^3 + 3b^2 - ab - 2a^2 + 2ab + 6b^2

    (ab = ba, so it's best to write all mixed terms in the same order)

    Now you need to collect like terms (otherwise you have just expanded the brackets not simplified them):

    3(a^2 + b^2) - a(b + 2a) +2b(a+3b) = (3a^3-2a^2) +(-ab+ 2ab) + (3b^2+6b^2) = a^2 + ab + 9b^2

    RonL
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