Divide x4 + 7 by x – 3.?

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  • It’s hard to write out “synthetic division” on Yahoo Answers. Here’s another way to divide a polynomial p(x) by (x-3). Add and subtract the multiple of (x-3) that has the same highest-power term as p(x), then simplify to get a smaller-degree polynomial r(x) plus multiple of (x-3).

    The multiple of (x-3) that has x^4 as its leading term is x^3(x-3) = x^4 – 3x^3. So write:

    x^4 + 7 = x^4 + 7 + x^3(x – 3) – x^3(x – 3)

    = x^4 + 7 + x^3(x – 3) – x^4 + 3x^3

    = x^3(x – 3) + 3x^3 + 7

    That makes r(x) = 3x^3 + 7. Do the same thing to reduce r(x) by adding/subtracting 3x^2(x – 3) = 3x^3 – 9x^2:

    = x^3(x – 3) + 3x^3 + 7 + 3x^2(x – 3) – (3x^3 – 9x^2)

    = x^3(x – 3) + 3x^2(x – 3) + 9x^2 + 7

    Again to reduce 9x^2 + 7:

    = x^3(x – 3) + 3x^2(x – 3) + 9x^2 + 7 + 9x(x – 3) – (9x^2 – 27x)

    = x^3(x – 3) + 3x^2(x – 3) + 9x(x – 3) + 27x + 7

    And finally write 27x + 7 as 27(x – 3) + 88;

    x^4 + 7 = x^3(x – 3) + 3x^2(x – 3) + 9x(x – 3) + 27(x – 3) + 88

    Factor out (x – 3) in all but the +88 term:

    x^4 + 7 = (x – 3)(x^3 + 3x^2 + 9x + 27) + 88

    That means that:

    (x^4 + 7) / (x – 3) = x^3 + 3x^2 + 9x + 27 with a remainder of 88

  • You can either use the process of long division or synthetic division for this problem

    Both ways you get the same answer:

    x^3 + 3x^2 + 9x + 27

    Remainder: 88

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