Question:
Find the equation of a normal to the curve $y=x \log _{e} x$ which is parallel to the line $2 x-2 y+3=0$.
Solution:
finding the slope of the tangent by differentiating the curve
$\frac{\mathrm{dy}}{\mathrm{dx}}=\ln \mathrm{x}+1$
$m$ (tangent) $=\ln x+1$
normal is perpendicular to tangent so, $m_{1} m_{2}=-1$]
$m($ normal $)=-\frac{1}{\ln x+1}$
equation of normal is given by $y-y_{1}=m($ normal $)\left(x-x_{1}\right)$
now comparing the slope of normal with the given equation
$\mathrm{m}($ normal $)=1$
$-\frac{1}{\ln x+1}=1$
$x=\frac{1}{e^{2}}$
since this point lies on the curve, we can find $y$ by substituting $x$
$y=-\frac{2}{e^{2}}$
The equation of normal is given by
$y+\frac{2}{e^{2}}=x-\frac{1}{e^{2}}$