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Question
Math
Posted 10 months ago
Find the values of PP and QQ that make the following equality true.
12x(x+1)(x5)dx=Plnx+1+Qlnx5+CP=Q=
\begin{array}{l}
\int \frac{1-2 x}{(x+1)(x-5)} d x=P \cdot \ln |x+1|+Q \cdot \ln |x-5|+C \\
P=\square \\
Q=\square
\end{array}
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Answer from Sia
Posted 10 months ago
Solution by Steps
step 1
To find the values of PP and QQ, we need to compare the given integral with the standard form of the partial fraction decomposition
step 2
The integral 12x(x+1)(x5)dx\int \frac{1-2x}{(x+1)(x-5)} dx can be decomposed into partial fractions as Ax+1+Bx5\frac{A}{x+1} + \frac{B}{x-5}
step 3
To find AA and BB, we solve the equation 12x=A(x5)+B(x+1)1-2x = A(x-5) + B(x+1)
step 4
Setting x=1x=-1 gives A=12(1)15=36=12A = \frac{1-2(-1)}{-1-5} = \frac{3}{-6} = -\frac{1}{2}
step 5
Setting x=5x=5 gives B=12(5)5+1=96=32B = \frac{1-2(5)}{5+1} = \frac{-9}{6} = -\frac{3}{2}
step 6
The integral then becomes 12x+1dx+32x5dx\int \frac{-\frac{1}{2}}{x+1} dx + \int \frac{-\frac{3}{2}}{x-5} dx
step 7
Integrating gives 12lnx+132lnx5+C-\frac{1}{2} \ln|x+1| - \frac{3}{2} \ln|x-5| + C
step 8
Comparing with the given integral form, we find P=12P = -\frac{1}{2} and Q=32Q = -\frac{3}{2}
Answer
P=12P = -\frac{1}{2}, Q=32Q = -\frac{3}{2}
Key Concept
Partial Fraction Decomposition
Explanation
To integrate a rational function, we can decompose it into simpler fractions whose integrals are known, and then integrate each term separately.

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