Chapter 2: Problem 97
$$ f(x)=\frac{x^{2}\left(x^{2 n}-1\right)}{x^{2}-1} $$
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Chapter 2: Problem 97
$$ f(x)=\frac{x^{2}\left(x^{2 n}-1\right)}{x^{2}-1} $$
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\(\mathrm{f}(\mathrm{x})=(\mathrm{x} \bmod 2)^{2}+(\mathrm{x} \bmod 4)\) Points of discontinuity are \(\mathrm{x}=2,4,6,8\) Hence, \(\mathrm{C}\) is correct.
$\prod_{n=1}^{n} \cos \left(\frac{x}{2^{n}}\right)=\frac{\sin x}{2^{n} \sin \left(\frac{x}{2^{n}}\right)}$ Taking log \& differentiate w.rt, \(x\). $\sum_{n=1}^{n} \frac{1}{2^{n}} \tan \left(\frac{x}{2^{n}}\right)=\frac{1}{2^{n}} \frac{\cos \left(x / 2^{n}\right)}{\sin \left(\frac{x}{2^{n}}\right)}-\cot x .$ now, $\lim _{n \rightarrow \infty} \sum_{n=1}^{n} \frac{1}{2^{n}} \tan \left(\frac{x}{2^{n}}\right)=\frac{1}{x}-\cot x$ $\lim _{x \rightarrow \frac{\pi}{2}} \lim _{n \rightarrow \infty} \sum_{n=1}^{n} \frac{1}{2^{n}} \tan \left(\frac{x}{2^{n}}\right)=\frac{2}{\pi}$
$f(x)=\frac{\log _{\sin x} \cos ^{3} x}{\log _{\sin |3 x|} \cos \frac{x}{2}}, x \in\left(-\frac{\pi}{3}, \frac{\pi}{3}\right), \quad x \neq 0$ $=\frac{3 \log (1+\cos x-1)}{\log \left(1+\cos \frac{x}{2}-1\right)} \times \frac{\log (1+\sin |3 x|-1)}{\log (1+\sin |x|-1)}$ \(f(x)\) is discontinuous at \(x=\pm \frac{\pi}{6}\)
\(f(x)=[\tan x[\cot x]], x \in\left[\frac{\pi}{12}, \frac{\pi}{2}\right)\) As \(\cot \frac{\pi}{12}=\frac{\sqrt{3}+1}{\sqrt{3}-1}=3.7\) \(\cot \frac{\pi}{2}=0\) \([\cot x]=0,1,2,3\) Hence, \(f(x)\) is discontinuous whenever \([\cot x]=1,2,3\) Hence, \(\mathrm{C}\) is correct.
$\lim _{x \rightarrow 0} \frac{\sin ^{4}\left(\frac{1}{x}\right)-\sin ^{2}\left(\frac{1}{x}\right)+1}{\cos ^{4}\left(\frac{1}{x}\right)-\cos ^{2}\left(\frac{1}{x}\right)+1}$ $\lim _{x \rightarrow 0} \frac{-\sin ^{2}\left(\frac{1}{x}\right) \cos ^{2}\left(\frac{1}{x}\right)+1}{-\cos ^{2}\left(\frac{1}{x}\right) \sin ^{2}\left(\frac{1}{x}\right)+1}=1$
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