Divide $$$2 x^{3} + 15 x^{2} + 22 x - 11$$$ by $$$x^{2} + 8 x + 15$$$
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Find $$$\frac{2 x^{3} + 15 x^{2} + 22 x - 11}{x^{2} + 8 x + 15}$$$ using long division.
Solution
Write the problem in the special format:
$$$\begin{array}{r|r}\hline\\x^{2}+8 x+15&2 x^{3}+15 x^{2}+22 x-11\end{array}$$$
Step 1
Divide the leading term of the dividend by the leading term of the divisor: $$$\frac{2 x^{3}}{x^{2}} = 2 x$$$.
Write down the calculated result in the upper part of the table.
Multiply it by the divisor: $$$2 x \left(x^{2}+8 x+15\right) = 2 x^{3}+16 x^{2}+30 x$$$.
Subtract the dividend from the obtained result: $$$\left(2 x^{3}+15 x^{2}+22 x-11\right) - \left(2 x^{3}+16 x^{2}+30 x\right) = - x^{2}- 8 x-11$$$.
$$\begin{array}{r|rrrr:c}&{\color{Chartreuse}2 x}&&&&\\\hline\\{\color{Magenta}x^{2}}+8 x+15&{\color{Chartreuse}2 x^{3}}&+15 x^{2}&+22 x&-11&\frac{{\color{Chartreuse}2 x^{3}}}{{\color{Magenta}x^{2}}} = {\color{Chartreuse}2 x}\\&-\phantom{2 x^{3}}&&&&\\&2 x^{3}&+16 x^{2}&+30 x&&{\color{Chartreuse}2 x} \left(x^{2}+8 x+15\right) = 2 x^{3}+16 x^{2}+30 x\\\hline\\&&- x^{2}&- 8 x&-11&\end{array}$$Step 2
Divide the leading term of the obtained remainder by the leading term of the divisor: $$$\frac{- x^{2}}{x^{2}} = -1$$$.
Write down the calculated result in the upper part of the table.
Multiply it by the divisor: $$$- \left(x^{2}+8 x+15\right) = - x^{2}- 8 x-15$$$.
Subtract the remainder from the obtained result: $$$\left(- x^{2}- 8 x-11\right) - \left(- x^{2}- 8 x-15\right) = 4$$$.
$$\begin{array}{r|rrrr:c}&2 x&{\color{GoldenRod}-1}&&&\\\hline\\{\color{Magenta}x^{2}}+8 x+15&2 x^{3}&+15 x^{2}&+22 x&-11&\\&-\phantom{2 x^{3}}&&&&\\&2 x^{3}&+16 x^{2}&+30 x&&\\\hline\\&&{\color{GoldenRod}- x^{2}}&- 8 x&-11&\frac{{\color{GoldenRod}- x^{2}}}{{\color{Magenta}x^{2}}} = {\color{GoldenRod}-1}\\&&-\phantom{- x^{2}}&&&\\&&- x^{2}&- 8 x&-15&{\color{GoldenRod}-1} \left(x^{2}+8 x+15\right) = - x^{2}- 8 x-15\\\hline\\&&&&4&\end{array}$$Since the degree of the remainder is less than the degree of the divisor, we are done.
The resulting table is shown once more:
$$\begin{array}{r|rrrr:c}&{\color{Chartreuse}2 x}&{\color{GoldenRod}-1}&&&\text{Hints}\\\hline\\{\color{Magenta}x^{2}}+8 x+15&{\color{Chartreuse}2 x^{3}}&+15 x^{2}&+22 x&-11&\frac{{\color{Chartreuse}2 x^{3}}}{{\color{Magenta}x^{2}}} = {\color{Chartreuse}2 x}\\&-\phantom{2 x^{3}}&&&&\\&2 x^{3}&+16 x^{2}&+30 x&&{\color{Chartreuse}2 x} \left(x^{2}+8 x+15\right) = 2 x^{3}+16 x^{2}+30 x\\\hline\\&&{\color{GoldenRod}- x^{2}}&- 8 x&-11&\frac{{\color{GoldenRod}- x^{2}}}{{\color{Magenta}x^{2}}} = {\color{GoldenRod}-1}\\&&-\phantom{- x^{2}}&&&\\&&- x^{2}&- 8 x&-15&{\color{GoldenRod}-1} \left(x^{2}+8 x+15\right) = - x^{2}- 8 x-15\\\hline\\&&&&4&\end{array}$$Therefore, $$$\frac{2 x^{3} + 15 x^{2} + 22 x - 11}{x^{2} + 8 x + 15} = \left(2 x - 1\right) + \frac{4}{x^{2} + 8 x + 15}$$$.
Answer
$$$\frac{2 x^{3} + 15 x^{2} + 22 x - 11}{x^{2} + 8 x + 15} = \left(2 x - 1\right) + \frac{4}{x^{2} + 8 x + 15}$$$A