If $y=\left(\frac{x^{2}}{x+1}\right)^{x}$ and $\frac{d y}{d x}=y\left[g(x)+\log…
If $y=\left(\frac{x^{2}}{x+1}\right)^{x}$ and $\frac{d y}{d x}=y\left[g(x)+\log \left(\frac{x^{2}}{x+1}\right)\right]$, then $g(x)=$
- $\frac{x+2}{x+1}$
- $x \log \left(\frac{x^{2}}{x+1}\right)$
- $\frac{x^{2}}{x+1}$
- $\frac{x-1}{x+2}$
Solution
1. Express $y$ in terms of exponentials:
$y=\left(\frac{x^2}{x+1}\right)^x=e^{x \log \left(\frac{x^2}{x+1}\right)}$
2. Differentiate $y$ using the chain rule: Taking the natural logarithm of both sides:
$\ln (y)=x \log \left(\frac{x^2}{x+1}\right)$
Differentiating both sides with respect to $x$ :
$\frac{1}{y} \frac{d y}{d x}=\frac{d}{d x}\left[x \log \left(\frac{x^2}{x+1}\right)\right] .$
3. Differentiate $x \log \left(\frac{x^2}{x+1}\right)$ : Using the product rule:
$\frac{d}{d x}\left[x \log \left(\frac{x^2}{x+1}\right)\right]=\log \left(\frac{x^2}{x+1}\right)+x \cdot \frac{d}{d x} \log \left(\frac{x^2}{x+1}\right)$
Simplify:
$\frac{d}{d x}\left[x \log \left(\frac{x^2}{x+1}\right)\right]=\log \left(\frac{x^2}{x+1}\right)+\frac{x+2}{x+1}$
6. Relate to the given equation: Substituting $\frac{1}{y} \frac{d y}{d x}$ :
$\frac{1}{y} \frac{d y}{d x}=\log \left(\frac{x^2}{x+1}\right)+\frac{x+2}{x+1}$
Comparing this with the given form:
$\frac{1}{y} \frac{d y}{d x}=g(x)+\log \left(\frac{x^2}{x+1}\right)$
we find:
$g(x)=\frac{x+2}{x+1}$
Asked in: MHT CET 2020 (13 Oct Shift 2)
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