Class CBSE Class 12 Mathematics Integrals Q #897
KNOWLEDGE BASED
APPLY
3 Marks 2023 SA
26. Find: $\int\frac{x^{2}+x+1}{(x+1)^{2}(x+2)}dx$

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Step-by-Step Solution

Let's decompose the integrand into partial fractions:

$\frac{x^2 + x + 1}{(x+1)^2(x+2)} = \frac{A}{x+1} + \frac{B}{(x+1)^2} + \frac{C}{x+2}$

Multiplying both sides by $(x+1)^2(x+2)$, we get:

$x^2 + x + 1 = A(x+1)(x+2) + B(x+2) + C(x+1)^2$

Expanding the terms:

$x^2 + x + 1 = A(x^2 + 3x + 2) + B(x+2) + C(x^2 + 2x + 1)$

$x^2 + x + 1 = Ax^2 + 3Ax + 2A + Bx + 2B + Cx^2 + 2Cx + C$

Grouping like terms:

$x^2 + x + 1 = (A+C)x^2 + (3A+B+2C)x + (2A+2B+C)$

Comparing coefficients, we get the following system of equations:

1) $A + C = 1$

2) $3A + B + 2C = 1$

3) $2A + 2B + C = 1$

From equation (1), $C = 1 - A$. Substituting this into equations (2) and (3):

2) $3A + B + 2(1-A) = 1 \Rightarrow A + B = -1$

3) $2A + 2B + (1-A) = 1 \Rightarrow A + 2B = 0$

Solving the system of equations $A + B = -1$ and $A + 2B = 0$, we get:

Subtracting the first equation from the second, we get $B = 1$.

Substituting $B = 1$ into $A + B = -1$, we get $A = -2$.

Since $C = 1 - A$, we have $C = 1 - (-2) = 3$.

Thus, $A = -2$, $B = 1$, and $C = 3$.

So, $\frac{x^2 + x + 1}{(x+1)^2(x+2)} = \frac{-2}{x+1} + \frac{1}{(x+1)^2} + \frac{3}{x+2}$

Now, we integrate:

$\int \frac{x^2 + x + 1}{(x+1)^2(x+2)} dx = \int \left( \frac{-2}{x+1} + \frac{1}{(x+1)^2} + \frac{3}{x+2} \right) dx$

$= -2 \int \frac{1}{x+1} dx + \int \frac{1}{(x+1)^2} dx + 3 \int \frac{1}{x+2} dx$

$= -2 \ln|x+1| - \frac{1}{x+1} + 3 \ln|x+2| + C$

Combining the logarithmic terms:

$= \ln\left| \frac{(x+2)^3}{(x+1)^2} \right| - \frac{1}{x+1} + C$

Correct Answer: -2 ln|x+1| - 1/(x+1) + 3 ln|x+2| + C

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Pedagogical Audit
Bloom's Analysis: This is an APPLY question because it requires students to apply the techniques of partial fraction decomposition and integration to solve the problem.
Knowledge Dimension: PROCEDURAL
Justification: The question requires the student to follow a specific procedure (partial fraction decomposition, followed by integration) to arrive at the solution.
Syllabus Audit: In the context of CBSE Class 12, this is classified as KNOWLEDGE. The question directly tests the student's knowledge of integration techniques and partial fraction decomposition, which are standard topics covered in the textbook.