Chapter 4: Problem 48
\((f(x))^{n}=f(n x)\) Differentiating it \((f(x))^{n-1} f^{\prime}(x)=f^{\prime}(n x)\) Multiply by \(f(x)\) $\mathrm{f}(\mathrm{nx}) \mathrm{f}^{\prime}(\mathrm{x})=\mathrm{f}^{\prime}(\mathrm{nx}) \mathrm{f}(\mathrm{x})$
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Chapter 4: Problem 48
\((f(x))^{n}=f(n x)\) Differentiating it \((f(x))^{n-1} f^{\prime}(x)=f^{\prime}(n x)\) Multiply by \(f(x)\) $\mathrm{f}(\mathrm{nx}) \mathrm{f}^{\prime}(\mathrm{x})=\mathrm{f}^{\prime}(\mathrm{nx}) \mathrm{f}(\mathrm{x})$
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\(y=\log _{e^{t}}(x-2)^{2}\) \(y=\frac{2 \log (x-2)}{\log x}\) $y^{\prime}=\frac{2(\log x) \times \frac{1}{x-2}-2 \log (x-2) \times \frac{1}{x}}{(\log x)^{2}}$ \(y^{\prime}=\frac{2}{\log 3}\) at \(x=3\)
If \(\mathrm{f}(\mathrm{x})=|\ln | \mathrm{x} \|\), then \(\mathrm{f}^{\prime}(\mathrm{x})\) equals (A) \(\frac{-\operatorname{sgn} \mathrm{x}}{|\mathrm{x}|}\), for \(|\mathrm{x}|<1\), where \(\mathrm{x} \neq 0\) (B) \(\frac{1}{x}\) for \(|x|>1\) and \(-\frac{1}{x}\) for \(|x|<1, x \neq 0\) (C) \(-\frac{1}{x}\) for \(|x|>1\) and \(\frac{1}{x}\) for \(|x|<1\) (D) \(\frac{1}{x}\) for \(|x|>0\) and \(-\frac{1}{x}\) for \(x<0\)
\(3 \mathrm{f}(\cos x)+2 f(\sin x)=5 x\) Put \(x=\frac{\pi}{2}-x\) \(3 \mathrm{f}(\sin x)+2 f(\cos x)=\frac{5 \pi}{2}-5 x\) Solving (I) \& (II) \(5 f(\cos x)=25 x-5 \pi\) \(f(\cos x)=5 x-\pi\) \(f^{\prime}(\cos x)=\frac{-5}{\sin x}\)
$\lim _{x \rightarrow 1} \frac{n x^{n+1}-(n+1) x^{n}+1}{\left(e^{x}-e\right) \sin \pi x}$ $\lim _{h \rightarrow 0} \frac{n(1+h)^{n+1}-(n+1)(1+h)^{n}+1}{-e\left(e^{h}-1\right) \sin \pi h}$ $\lim _{\mathrm{h} \rightarrow 0} \frac{\mathrm{n}(1+\mathrm{h})^{\mathrm{n}+1}-(\mathrm{n}+1)(1+\mathrm{h})^{\mathrm{n}}+1}{-\pi \mathrm{t} \mathrm{h}^{2}}$ $\lim _{\mathrm{h} \rightarrow 0} \frac{\mathrm{n}(\mathrm{n}+1)(1+\mathrm{h})^{\mathrm{n}}-\mathrm{n}(\mathrm{n}+1)(1+\mathrm{h})^{\mathrm{n}-1}}{-2 \pi \mathrm{t} h}$ $\lim _{\mathrm{h} \rightarrow 0} \frac{\mathrm{n}(\mathrm{n}+1)(\mathrm{n})(1+\mathrm{h})^{\mathrm{n}-1}-\mathrm{n}(\mathrm{n}+1)(1+\mathrm{h})^{\mathrm{n}-2}(\mathrm{n}-1)}{-2 \pi \mathrm{e}}$ $=\frac{\mathrm{n}^{2}(\mathrm{n}+1)-\mathrm{n}(\mathrm{n}-1)}{-2 \pi \mathrm{e}}(\mathrm{n}+1)=\frac{\mathrm{n}(\mathrm{n}+1)}{-2 \pi \mathrm{e}}$ Put \(\mathrm{n}=100\) \(=\frac{-5050}{\pi \mathrm{e}}\)
$\frac{f(2 x+2 y)-f(2 x-2 y)}{f(2 x+2 y)+f(2 x-2 y)}=\frac{\cos x \sin y}{\sin x \cos y}$ Applying C \& D, $\frac{\mathrm{f}(2 \mathrm{x}+2 \mathrm{y})}{\mathrm{f}(2 \mathrm{x}-2 \mathrm{y})}=\frac{\sin (\mathrm{x}+\mathrm{y})}{\sin (\mathrm{x}-\mathrm{y})}$ \(\frac{\mathrm{f}(2 \mathrm{x}+2 \mathrm{y})}{\sin (\mathrm{x}+\mathrm{y})}\) is constant \(\Rightarrow \mathrm{f}(\mathrm{x})=\mathrm{C} \sin \frac{\mathrm{x}}{2}\) \(\mathrm{C}=1\) using \(\mathrm{f}^{\prime}(0)=\frac{1}{2}\) \(\Rightarrow \mathrm{f}(\mathrm{x})=\sin \frac{\mathrm{x}}{2}\) \(\mathrm{f}^{\prime}(\mathrm{x})=\frac{1}{2} \cos \frac{\mathrm{x}}{2}\) $\mathrm{f}^{\prime \prime}(\mathrm{x})=\frac{-1}{4} \sin \frac{\mathrm{x}}{2}$ $\Rightarrow 4 \mathrm{f}^{\prime \prime}(\mathrm{x})+\mathrm{f}(\mathrm{x})=0$
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