Medium MCQ +4 / -1 PYQ · JEE Mains 2023

Let $\alpha \in (0,1)$ and $\beta = {\log _e}(1 - \alpha )$. Let $${P_n}(x) = x + {{{x^2}} \over 2} + {{{x^3}} \over 3}\, + \,...\, + \,{{{x^n}} \over n},x \in (0,1)$$. Then the integral $\int\limits_0^\alpha {{{{t^{50}}} \over {1 - t}}dt}$ is equal to

  1. A $- \left( {\beta + {P_{50}}\left( \alpha \right)} \right)$ Correct answer
  2. B $\beta - {P_{50}}(\alpha )$
  3. C ${P_{50}}(\alpha ) - \beta$
  4. D $\beta + {P_{50}} - (\alpha )$

Solution

$\int_{0}^{\alpha} \frac{t^{50}}{1-t} d t$ <br/><br/>$$ \begin{aligned} & = \int_{0}^{\alpha} \frac{t^{50}-1+1}{1-t}\\\\ & =-\int_{0}^{\alpha}\left(\frac{1-t^{50}}{1-t}-\frac{1}{1-t}\right) d t\\\\ & =-\int_{0}^{\alpha}\left(1+t+\ldots . .+t^{49}\right)+\int_{0}^{\alpha} \frac{1}{1-t} d t \end{aligned} $$ <br/><br/>$=-\left(\frac{\alpha^{50}}{50}+\frac{\alpha^{49}}{49}+\ldots . .+\frac{\alpha^{1}}{1}\right)+\left(\frac{\ln (1-\mathrm{f})}{-1}\right)_{0}^{\alpha}$ <br/><br/>$=-\mathrm{P}_{50}(\alpha)-\ln (1-\alpha)$ <br/><br/>$=-\mathrm{P}_{50}(\alpha)-\beta$

About this question

Subject: Mathematics · Chapter: Definite Integration · Topic: Properties of Definite Integrals

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