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CBSE Class 12 Math 2008 Solved Paper

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Question : 14 of 29
Marks: +1, -0
For what value of k is the following function continuous at x = 2?
f (x) = {2x+1,x<2k,x=23x1,x>2\left\{ \begin{array}{l} 2x+1, x < 2 \\ k, x = 2 \\ 3x-1, x > 2 \end{array} \right.
Solution:  
The given function f(x) will be continuous at x = 2, if
limx2\lim\limits_{x\rightarrow2^{-}} f (x) = limx2+\lim\limits_{x\rightarrow2^{+}} f (x) = f (2)
limx2\lim\limits_{x\rightarrow2^{-}} = limx2\lim\limits_{x\rightarrow2^{-}} 2x + 1 = 2 × 2 + 1 = 5
limx2\lim\limits_{x\rightarrow2^{-}} = limx2\lim\limits_{x\rightarrow2^{-}} 3x + 1 = 3 × 2 - 1 = - 5
∴ f (2) = k
⇒ k = 5
Thus, for k = 5, the given function is continuous at x = 2.
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