Q. Use synthetic division to divide \(3x^3 – 11x^2 + 16x – 30\) by \(x – 3\).

Answer

\[
\begin{array}{r|rrrr}
3 & 3 & -11 & 16 & -30\\\hline
& & 9 & -6 & 30\\
& 3 & -2 & 10 & 0
\end{array}
\]

Bring down 3, multiply by 3 → 9, add → -2, multiply by 3 → -6, add → 10, multiply by 3 → 30, add → 0.

Quotient: \(3x^{2}-2x+10\), remainder: \(0\).

Detailed Explanation

Synthetic division of the polynomial by x−3 — step-by-step

  1. Write the polynomial and identify the divisor root.The dividend is \(3x^{3}-11x^{2}+16x-30\). The divisor is \(x-3\), whose root is \(3\).
  2. List the coefficients and set up the synthetic division table.The coefficients of the dividend (from highest degree to constant) are 3, −11, 16, −30. Place the root 3 to the left and the coefficients in a row:
    3 |  3   -11    16   -30
      |       9    -6    30
      ---------------------
         3    -2    10     0
    

    The numbers that will be written on the lower row are produced by the synthetic division steps shown next.

  3. Step-by-step operations (each operation explained separately).
    1. Bring down the first coefficient.Bring down the leading coefficient 3 to the bottom row. This becomes the first coefficient of the quotient.

      Bottom row first entry: \(3\).

    2. Multiply and add to get the next bottom entry.Multiply the bottom entry 3 by the root 3: \(3 \times 3 = 9\).

      Add this product to the next coefficient in the top row: \(-11 + 9 = -2\).

      Bottom row second entry: \(-2\).

    3. Repeat multiply and add.Multiply the new bottom entry \(-2\) by the root 3: \(-2 \times 3 = -6\).

      Add to the next coefficient: \(16 + (-6) = 10\).

      Bottom row third entry: \(10\).

    4. Final multiply and add to obtain the remainder.Multiply the bottom entry 10 by the root 3: \(10 \times 3 = 30\).

      Add to the final coefficient: \(-30 + 30 = 0\).

      The final bottom entry is the remainder: \(0\).

  4. Form the quotient and state the remainder.The bottom row entries (except the final remainder) are the coefficients of the quotient polynomial, in descending powers of x. They are \(3\), \(-2\), and \(10\), which correspond to the quotient

    \(3x^{2} – 2x + 10\).

    The remainder is \(0\).

    Therefore, dividing \(3x^{3}-11x^{2}+16x-30\) by \(x-3\) yields the quotient \(3x^{2}-2x+10\) with remainder \(0\).

  5. Optional check (value at the root).Evaluate the polynomial at \(x=3\) to confirm the remainder is zero:

    \(f(3)=3(3)^{3}-11(3)^{2}+16(3)-30=81-99+48-30=0\).

    This confirms the remainder is \(0\) and that \(x-3\) is a factor.

Final result: Quotient is \(3x^{2}-2x+10\) and remainder is \(0\).

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Algebra FAQs

What is synthetic division?

Synthetic division is a shortcut method for dividing a polynomial by a linear divisor \(x-c\). It uses only the coefficients and repeated multiplication/addition to produce the quotient coefficients and remainder faster than long division..

How do I set up synthetic division for \(3x^3-11x^2+16x-30\) divided by \(x-3\)?

Write the coefficients \( [3, -11, 16, -30] \) and use \(c=3\). Bring down 3, multiply by 3, add vertically, repeat across; final row gives quotient coefficients and remainder..

What is the quotient and remainder for this division?

The quotient is \(3x^2-2x+10\) and the remainder is \(0\). So \(3x^3-11x^2+16x-30=(x-3)(3x^2-2x+10)\).

What if the polynomial has a missing term, e.g., no \(x^2\) term?.

Insert a zero coefficient for any missing power. For example, divide \(x^3+2x-5\) by \(x-1\) using coefficients [1,0,2,-5].

Why do we use \(c=3\) for divisor \(x-3\)?

For a divisor \(x-c\), synthetic division uses \(c\). Setting \(x-c=0\) gives \(x=c\), which is the number used for the synthetic process.

How does synthetic division connect to the Remainder and Factor Theorems?

How does synthetic division connect to the Remainder and Factor Theorems?

Can synthetic division be used when the divisor is not of the form \(x-c\)?

Standard synthetic division only works for linear divisors \(x-c\). For other linear forms \(ax-b\), first factor out the leading coefficient or use polynomial long division or an adapted synthetic method.

What if the leading coefficient isn’t 1 — does synthetic division still work?

Yes. Synthetic division works for any leading coefficient; you still use the polynomial's coefficients directly. The quotient coefficients reflect the original leading coefficient (as in this problem, leading \(3\) produced quotient starting with \(3\)).
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