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Polynomial Long Division: Examples (page 3 of 3)

Sections: Simplification and reduction, Polynomial long division


  • Simplify  (x^2 + 9x + 1)/(x + 7)

    This can be done in either of two ways. If you know how to factor quadratics, you can factor the top and then cancel the common factor, like this:

      (x + 2)(x + 7)/(x + 7) = x + 2

    But what if you don't know how to factor? You can always use long division:

      animation

    (Don't forget to change your signs, as shown in red.)

    The answer is the polynomial across the top:  x + 2

  • Divide 3x3 – 5x2 + 10x – 3  by  3x + 1
    • animation

    This division did not come out even. What am I supposed to do with the remainder?

    Think back to when you did long division with plain numbers. Sometimes there would be a remainder; for instance, if you divide 132 by 5:

      long division

    ...there is a remainder of 2. Remember how you handled that? You made a fraction, putting the remainder on top of the divisor, and wrote the answer as "twenty-six and two-fifths":

      132/5 = 26 + 2/5

    You do the same thing with polynomial division. Since the remainder is –7 and since the divisor is 3x + 1, then turn this into a fraction and add it (don't multiply it) to the polynomial across the top of the division symbol. Since the division looks like this:

      animation

    ...then the answer is this:   Copyright © Elizabeth Stapel 2006-2008 All Rights Reserved

       x^2 - 2x + 4 + (-7)/(3x + 1)

  • Divide 2x3 – 9x2 + 15  by  2x – 5

    Note that there is a gap in the degrees of the terms of the dividend: the first polynomial has no x term. It can get very messy inside the division symbol, so it is very important that you leave space for a x-term column. You can do this by turning the dividend into 2x3 – 9x2 + 0x + 15. Then do the division:

      animation

    I need to remember to add the remainder to the polynomial part of the answer:

        x^2 - 2x - 5 + (-10)/(2x - 5)

  • Divide 4x4 + 3x3 + 2x + 1  by x2 + x + 2
    • animation

    The answer is:

       4x^2 - x - 7 + (11x + 15)/(x^2 + x + 2)

Write neatly, remember to change your signs, and work carefully. These problems should not be very hard. Annoying, maybe, but not hard. Just take your time.

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Cite this article as:

Stapel, Elizabeth. "Polynomial Long Division: Examples." Purplemath. Available from
    http://www.purplemath.com/modules/polydiv3.htm. Accessed
 

 

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