At any point $(x, y)$ of a curve, the slope of the tangent is twice the slope of the line segment joining the point of contact to the point
At any point $(x, y)$ of a curve, the slope of the tangent is twice the slope of the line segment joining the point of contact to the point $(-4,-3)$. Find the equation of the curve given that it passes through $(-2,1)$.
It is given that (x, y) is the point of contact of the curve and its tangent.
The slope $\left(m_{1}\right)$ of the line segment joining $(x, y)$ and $(-4,-3)$ is $\frac{y+3}{x+4}$.
We know that the slope of the tangent to the curve is given by the relation,
$\frac{d y}{d x}$
$\therefore$ Slope $\left(m_{2}\right)$ of the tangent $=\frac{d y}{d x}$
According to the given information:
$m_{2}=2 m_{1}$
$\Rightarrow \frac{d y}{d x}=\frac{2(y+3)}{x+4}$
$\Rightarrow \frac{d y}{y+3}=\frac{2 d x}{x+4}$
Integrating both sides, we get:
$\int \frac{d y}{y+3}=2 \int \frac{d x}{x+4}$
$\Rightarrow \log (y+3)=2 \log (x+4)+\log \mathrm{C}$
$\Rightarrow \log (y+3) \log \mathrm{C}(x+4)^{2}$
$\Rightarrow y+3=\mathrm{C}(x+4)^{2}$ ....(1)
This is the general equation of the curve.
It is given that it passes through point (–2, 1).
$\Rightarrow 1+3=C(-2+4)^{2}$
$\Rightarrow 4=4 C$
$\Rightarrow C=1$
Substituting C = 1 in equation (1), we get:
$y+3=(x+4)^{2}$
This is the required equation of the curve.