Class CBSE Class 12 Mathematics Definite Integrals Q #1706
COMPETENCY BASED
APPLY
1 Marks 2026 AISSCE(Board Exam) MCQ SINGLE
If $\int_{0}^{1}\frac{dx}{e^{x}+e^{-x}}=\tan^{-1}e+k$, then the value of k is:
(A) e
(B) $\frac{\pi}{4}$
(C) $0$
(D) $-\frac{\pi}{4}$
Correct Answer: D

AI Tutor Explanation

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Detailed Solution

Step 1: Simplify the integrand

The given integral is $I = \int_{0}^{1}\frac{dx}{e^{x}+e^{-x}}$. Multiply the numerator and denominator by $e^{x}$ to rewrite the expression: $$I = \int_{0}^{1}\frac{e^{x}}{e^{2x}+1} dx$$

Step 2: Apply substitution

Let $u = e^{x}$. Then $du = e^{x} dx$. When $x = 0$, $u = e^{0} = 1$. When $x = 1$, $u = e^{1} = e$. The integral becomes: $$I = \int_{1}^{e}\frac{du}{u^{2}+1}$$

Step 3: Evaluate the definite integral

The integral of $\frac{1}{u^{2}+1}$ is $\tan^{-1}(u)$. Applying the limits: $$I = [\tan^{-1}(u)]_{1}^{e} = \tan^{-1}(e) - \tan^{-1}(1)$$ Since $\tan^{-1}(1) = \frac{\pi}{4}$, we have: $$I = \tan^{-1}(e) - \frac{\pi}{4}$$

Step 4: Solve for k

Equating our result to the given expression $\tan^{-1}(e) + k$: $$\tan^{-1}(e) - \frac{\pi}{4} = \tan^{-1}(e) + k$$ Therefore, $k = -\frac{\pi}{4}$.

Final Answer: $-\frac{\pi}{4}$

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Pedagogical Audit
Bloom's Analysis: This is an APPLY question because it requires the student to manipulate the integrand using algebraic techniques and apply the method of substitution to solve a definite integral.
Knowledge Dimension: PROCEDURAL
Justification: The student must follow a specific sequence of mathematical steps (algebraic manipulation, substitution, and evaluation of limits) to reach the solution.
Syllabus Audit: In the context of CBSE Class 12, this is classified as COMPETENCY. This question tests the student's ability to recognize standard integral forms hidden behind algebraic transformations, which is a core competency in the Calculus unit.