Question:
If the tangent line at a point $(x, y)$ on the curve $y=f(x)$ is parallel to $x$-axis, then write the value of $\frac{d y}{d x}$.
Solution:
Given curve $y=f(x)$ has a point $(x, y)$ which is parallel to $x$-axis.
We know that the slope of the $x$-axis is $0 .$
$\because$ the point lies on the given curve
$\therefore$ Slope of the tangent $\frac{d y}{d x}=0$