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Math Help - Remainder Theorum

  1. #1
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    Remainder Theorum

    hi all,

    could some please help with the following question.

    The remainder when 2x^3 + ax^2 + 4 is dividied by x - 2 is five times more that when it is divided by x - 1.
    Find a.

    As far as i can see ( i remember to set x to a value that makes divisor 0 since dividend=divisor x quotient + remainder) :

    f(x)=2x^3+ax^2+4

    f(1)=2+a+4

    f(2)=16+4a+4

    and

    f(2)=5f(1)

    20+4a = 5(6+a)

    20+4a=30+5a

    -10=a

    must be doing something stupid because the book says the answer is -3
    thanks sammy
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  2. #2
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    Everything is correct... Either your book's answer is wrong or you have copied the question incorrectly.
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  3. #3
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    thanks for checking it Prove It.
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