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Math Help - The Remainder Theorem question

  1. #1
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    The Remainder Theorem question

    Hey guys I am a bit stuck on how to do this question. Could you please go through step-by-step on how to get the answer! Thank You!

    "The Remainder when x^3-2x^2+ax+5 is divided by x-3 is twice the remainder when the same expression is divided by x+1. Find the constant value of a."

    I started off like: f(3)=2(x-1) but I am not sure if that is correct or not because I didn't get the right answer. Am I along the right lines but there are more steps or am I off the line completely? Once I can do this question I can answer some of the other questions which is a similar style to this.

    Thanks

    DantheMaths
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  2. #2
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    Re: The Remainder Theorem question

    Quote Originally Posted by Danthemaths View Post
    "The Remainder when x^3-2x^2+ax+5 is divided by x-3 is twice the remainder when the same expression is divided by x+1. Find the constant value of a."
    f(3)=27-18+3a+5~\&~f(-1)=-1-2-a+5.
    Now finish.
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  3. #3
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    Re: The Remainder Theorem question

    i did do that but for f(3) i got -14=3a cant remember what exactly and for f(-1) i got 2. I looked at the answer and it says the answer is 4! how can i possibly get to 4???
    Last edited by Danthemaths; October 18th 2012 at 08:27 AM.
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    Re: The Remainder Theorem question

    Quote Originally Posted by Danthemaths View Post
    Hey guys I am a bit stuck on how to do this question. Could you please go through step-by-step on how to get the answer! Thank You!
    "The Remainder when x^3-2x^2+ax+5 is divided by x-3 is twice the remainder when the same expression is divided by x+1. Find the constant value of a."
    I am not sure you understand this problem.
    The Remainder when f(x)=x^3-2x^2+ax+5 is divided by x-3 is f(3)

    The Remainder when f(x)=x^3-2x^2+ax+5 is divided by x+1 is f(-1)

    So f(3)=2f(-1). Solve for a
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