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Multiple Choice
Evaluate the indefinite integral as a power series:
A
B
C
D
Verified step by step guidance
1
Step 1: Recall the Taylor series expansion for arctan(x). The series is given by \( \arctan(x) = \sum_{n=0}^{\infty} \frac{(-1)^n}{2n+1} x^{2n+1} \). This will be the starting point for expressing \( \arctan(x) \) as a power series.
Step 2: Multiply the series representation of \( \arctan(x) \) by \( x \), as the integral involves \( \arctan(x) \cdot x \). This results in \( \arctan(x) \cdot x = \sum_{n=0}^{\infty} \frac{(-1)^n}{2n+1} x^{2n+2} \).
Step 3: Integrate term-by-term. The integral of \( x^{2n+2} \) is \( \frac{x^{2n+3}}{2n+3} \). Therefore, the integral becomes \( \int \arctan(x) \cdot x \; dx = \sum_{n=0}^{\infty} \frac{(-1)^n}{(2n+1)(2n+3)} x^{2n+3} + C \), where \( C \) is the constant of integration.
Step 4: Verify the result by differentiating the obtained series. Differentiating \( \sum_{n=0}^{\infty} \frac{(-1)^n}{(2n+1)(2n+3)} x^{2n+3} \) term-by-term should yield \( \arctan(x) \cdot x \), confirming the correctness of the integration.
Step 5: Compare the result with the given options. The correct answer matches \( \sum_{n=0}^{\infty} \frac{(-1)^n}{(2n+1)(2n+3)} x^{2n+3} + C \).