Question:
Find the point on the curve $y=x^{2}$ where the slope of the tangent is equal to the $x$-coordinate of the point.
Solution:
Let the required point be (x1, y1).
Given:
$y=x^{2}$
Point $\left(x_{1}, y_{1}\right)$ lies on a curve.
$\therefore y_{1}=x_{1}^{2} \quad \ldots(1)$
Now,
$y=x^{2} \Rightarrow \frac{d y}{d x}=2 x$
Slope of the tangent at $\left(x_{1}, y_{1}\right)=\left(\frac{d y}{d x}\right)_{\left(x_{1}, y_{1}\right)}=2 x_{1}$
Slope of the tangent $=x$ coordinate of the point $[$ Given $]$
$\therefore 2 x_{1}=x_{1}$
This happens only when $x_{1}=0$.
On putting $x_{1}=0$ in eq. (1), we get
$y_{1}=x_{1}^{2}=0^{2}=0$
Thus, the required point is $(0,0)$.