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

Let $y(x) = (1 + x)(1 + {x^2})(1 + {x^4})(1 + {x^8})(1 + {x^{16}})$. Then $y' - y''$ at $x = - 1$ is equal to

  1. A 496 Correct answer
  2. B 976
  3. C 464
  4. D 944

Solution

$$ \begin{aligned} & y=\frac{1-x^{32}}{1-x}=1+x+x^2+x^3+\ldots+x^{31} \\\\ & y^{\prime}=1+2 x+3 x^2+\ldots+31 x^{30} \\\\ & y^{\prime}(-1)=1-2+3-4+\ldots+31=16 \\\\ & y^{\prime \prime}(x)=2+6 x+12 x^2+\ldots+31.30 x^{29} \\\\ & y^{\prime \prime}(-1)=2-6+12 \ldots 31.30=480 \\\\ & y^{\prime \prime}(-1)-y^{\prime}(-1)=-496 \end{aligned} $$

About this question

Subject: Mathematics · Chapter: Differentiation · Topic: Derivatives of Standard Functions

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