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Lim X → − 1 / 2 8 X 3 + 1 2 X + 1 - Mathematics

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Question

\[\lim_{x \to - 1/2} \frac{8 x^3 + 1}{2x + 1}\] 

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Solution

\[\lim_{x \to - 1/2} \left[ \frac{8 x^3 + 1}{2x + 1} \right]\]
\[\text{ It is of the form } \frac{0}{0} . \]
\[ \lim_{x \to - 1/2} \left[ \frac{\left( 2x \right)^3 + 1}{2x + 1} \right]\]
\[ = \lim_{x \to - 1/2} \left[ \frac{\left( 2x + 1 \right)\left\{ \left( 2x \right)^2 - 2x \times 1 + 1^2 \right\}}{\left( 2x + 1 \right)} \right] \left[ \because A^3 + B^3 = \left( A + B \right)\left( A^2 - AB + B^2 \right) \right]\]
\[ = \lim_{x \to - 1/2} \left[ \left( 2x \right)^2 - 2x + 1 \right]\]
\[ = \left( 2 \times \frac{- 1}{2} \right)^2 - 2 \times \frac{- 1}{2} + 1\]
\[ = 1 + 1 + 1\]
\[ = 3\]

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Chapter 29: Limits - Exercise 29.3 [Page 23]

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RD Sharma Mathematics [English] Class 11
Chapter 29 Limits
Exercise 29.3 | Q 5 | Page 23

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