Question:
Find the points on the curve $y=x^{3}$ at which the slope of the tangent is equal to the $y$-coordinate of the point.
Solution:
The equation of the given curve is $y=x^{3}$.
$\therefore \frac{d y}{d x}=3 x^{2}$
The slope of the tangent at the point (x, y) is given by,
$\left.\frac{d y}{d x}\right]_{(x, y)}=3 x^{2}$
When the slope of the tangent is equal to the $y$-coordinate of the point, then $y=3 x^{2}$.
Also, we have $y=x^{3}$.
$\therefore 3 x^{2}=x^{3}$
$\Rightarrow x^{2}(x-3)=0$
$\Rightarrow x=0, x=3$
When $x=0$, then $y=0$ and when $x=3$, then $y=3(3)^{2}=27$.
Hence, the required points are (0, 0) and (3, 27).