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NCERT Class XI Mathematics - Limits and Derivatives - Solutions

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Question : 23 of 72
Marks: +1, -0
Find lim⁡x→0\lim\limits_{x\to 0} f (x) and lim⁡x→1\lim\limits_{x\to 1} f (x), where
f (x) = {2x−3,x≤03(x+1),x>0\begin{cases} 2x-3, & x \le 0 \\ 3(x+1), & x > 0 \end{cases}
Solution:  
We have, f (x) = {2x−3,x≤03(x+1),x>0\begin{cases} 2x-3, & x \le 0 \\ 3(x+1), & x > 0 \end{cases}
For lim⁡x→0\lim\limits_{x\to 0} f (x) , we have to evaluate lim⁡x→0−\lim\limits_{x\to 0^-} f (x) and lim⁡x→0+\lim\limits_{x\to 0^+} f (x) separately as f(x) is defined differently on left and right of 0.
Now, lim⁡x→0−\lim\limits_{x\to 0^-} f (x) = lim⁡x→0−\lim\limits_{x\to 0^-} (2x + 3) = 2 . (0) + 3 = 3
and lim⁡x→0+\lim\limits_{x\to 0^+} f (x) = lim⁡x→0+\lim\limits_{x\to 0^+} 3 (x + 1) = 3 (0 + 1) = 3.
Thus we see, lim⁡x→0−\lim\limits_{x\to 0^-} f (x) = lim⁡x→0+\lim\limits_{x\to 0^+} f (x) = 3
∴ lim⁡x→0\lim\limits_{x\to 0} f (x) = 3
Now, lim⁡x→1\lim\limits_{x\to 1} f (x) 3 (x + 1) = 3 × 2 = 6
∴ lim⁡x→1\lim\limits_{x\to 1} f (x) = 6 and lim⁡x→0\lim\limits_{x\to 0} f (x) = 3.
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