Question:
Write the equation of the tangent to the curve $y=x^{2}-x+2$ at the point where it crosses the $y$-axis.
Solution:
Given that the curve $y=x^{2}-x+2$ has a point crosses the $y$-axis.
The curve will be in the form of $(0, y)$
$\Rightarrow y=0-0+2$
$\Rightarrow y=2$
So, the point at which curve crosses the $y$-axis is $(0,2)$.
Now, differentiating the equation of curve w.r.t. $x$
$\frac{d y}{d x}=x-1$
For $(0,2)$,
$\frac{\mathrm{dy}}{\mathrm{dx}}=-1$
Equation of the tangent:
$\left(\mathrm{y}-\mathrm{y}_{1}\right)=$ Slope of tangent $\times\left(\mathrm{x}-\mathrm{x}_{1}\right)$
$\Rightarrow(y-2)=-1 \times(x-0)$
$\Rightarrow y-2=-x$
$\Rightarrow x+y=2$