High School

Complete the synthetic division problem below:

[tex]-1 \longdiv {2 \quad 7 \quad 5}[/tex]

What is the quotient in polynomial form?

A. [tex]x - 5[/tex]
B. [tex]x + 5[/tex]
C. [tex]2x + 5[/tex]
D. [tex]2x - 5[/tex]

Answer :

We need to divide the polynomial

[tex]$$2x^2 + 7x + 5$$[/tex]

by the linear divisor

[tex]$$x + 1,$$[/tex]

which means the zero of the divisor is [tex]$-1$[/tex]. The synthetic division process is as follows:

1. Write the coefficients of the polynomial: for [tex]$2x^2$[/tex], [tex]$7x$[/tex], and [tex]$5$[/tex], the coefficients are [tex]$2$[/tex], [tex]$7$[/tex], and [tex]$5$[/tex], respectively.

2. Set up the division using [tex]$-1$[/tex] (since [tex]$x+1=0$[/tex] gives [tex]$x=-1$[/tex]) on the left:

[tex]$$
\begin{array}{r|ccc}
-1 & 2 & 7 & 5 \\
\hline
& & &
\end{array}
$$[/tex]

3. Bring down the leading coefficient [tex]$2$[/tex]:

[tex]$$
\begin{array}{r|ccc}
-1 & 2 & 7 & 5 \\
\hline
& 2 & &
\end{array}
$$[/tex]

4. Multiply the number just written ([tex]$2$[/tex]) by [tex]$-1$[/tex] and write the result under the next coefficient:

[tex]$$2 \times (-1) = -2.$$[/tex]

So we have:

[tex]$$
\begin{array}{r|ccc}
-1 & 2 & 7 & 5 \\
\hline
& 2 & -2 & \\
\end{array}
$$[/tex]

5. Add the second coefficient [tex]$7$[/tex] and [tex]$-2$[/tex]:

[tex]$$7 + (-2) = 5.$$[/tex]

Write [tex]$5$[/tex] in the row below:

[tex]$$
\begin{array}{r|ccc}
-1 & 2 & 7 & 5 \\
\hline
& 2 & 5 & \\
\end{array}
$$[/tex]

6. Multiply the number just written ([tex]$5$[/tex]) by [tex]$-1$[/tex]:

[tex]$$5 \times (-1) = -5.$$[/tex]

Place it under the next coefficient:

[tex]$$
\begin{array}{r|ccc}
-1 & 2 & 7 & 5 \\
\hline
& 2 & 5 & -5 \\
\end{array}
$$[/tex]

7. Lastly, add the constant term [tex]$5$[/tex] and [tex]$-5$[/tex]:

[tex]$$5 + (-5) = 0.$$[/tex]

So the final row is:

[tex]$$
\begin{array}{r|ccc}
-1 & 2 & 7 & 5 \\
\hline
& 2 & 5 & 0 \\
\end{array}
$$[/tex]

The numbers in the bottom row (except the remainder) are the coefficients of the quotient. Since we started with a quadratic polynomial, the quotient is one degree lower, namely linear. Therefore, the quotient polynomial is:

[tex]$$2x + 5.$$[/tex]

This result corresponds to option C.