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NCERT Class XI Mathematics - Limits and Derivatives - Solutions

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Question : 26 of 72
Marks: +1, -0
Find lim⁡x→0\lim\limits_{x\to 0} f (x) , where f (x) = {x∣x∣,x≠00,x=0\begin{cases} \frac{x}{|x|}, & x \neq 0 \\ 0, & x = 0 \end{cases}
Solution:  
We have, f (x) = {x∣x∣,x≠00,x=0\begin{cases} \frac{x}{|x|}, & x \neq 0 \\ 0, & x = 0 \end{cases}
Now, lim⁡x→0−\lim\limits_{x\to 0^{-}} f (x) = lim⁡x→0−\lim\limits_{x\to 0^{-}} x∣x∣\frac{x}{|x|} = lim⁡x→0−\lim\limits_{x\to 0^{-}} (x−x)\left(\frac{x}{-x}\right) [Since |x| = - x , for x < 0]
= lim⁡x→0−\lim\limits_{x\to 0^{-}} ( - 1) = - 1
and lim⁡x→0+\lim\limits_{x\to 0^{+}} f (x) = lim⁡x→0+\lim\limits_{x\to 0^{+}} x∣x∣\frac{x}{|x|} = lim⁡x→0+\lim\limits_{x\to 0^{+}} xx\frac{x}{x} [Since |x| = x , for x > 0]
= lim⁡x→0+\lim\limits_{x\to 0^{+}} (1) = 1
Thus lim⁡x→0−\lim\limits_{x\to 0^{-}} f (x) ≠ lim⁡x→0+\lim\limits_{x\to 0^{+}} f (x)
∴ lim⁡x→0\lim\limits_{x\to 0} f (x) does not exist.
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