Practicing Success
The equation of the curve passing through the origin and satisfying the differential equation $\left(\frac{d y}{d x}\right)^2=(x-y)^2$, is |
$e^{2 x}(1-x+y)=1+x-y$ $e^{2 x}(1+x-y)=1-x+y$ $e^{2 x}(1-x+y)=1+x+y$ $e^{2 x}(1+x+y)=1-x+y$ |
$e^{2 x}(1-x+y)=1+x-y$ |
We have, $\frac{d y}{d x}= \pm(x-y)$ CASE I: When $\frac{d y}{d x}=(x-y)$ In this case, we have $1-\frac{d v}{d x}=v$, where $x-y=v$ $\Rightarrow \frac{d v}{d x}=1-v$ $\Rightarrow \frac{1}{1-v} d v=d x$ $\Rightarrow -\log (1-v)=x+\log C$ $\Rightarrow (1-v)^{-1}=C e^x \Rightarrow \frac{1}{1-x+y}=C e^x$ It passes through the origin. ∴ $C=1$ Hence, $\frac{1}{1-x+y}=e^x$ ......(i) CASE II: When $\frac{d y}{d x}=-(x-y)=y-x$ In this case, we have $\frac{d u}{d x}+1=u$, where $u=y-x$ $\Rightarrow \frac{d u}{u-1}=d x$ $\Rightarrow \log (u-1)=x+\log C$ $\Rightarrow u-1=C e^x \Rightarrow y-x-1=C e^x$ It passes through the origin. ∴ $C=-1$ Hence, $y-x-1=-e^x$ or, $x-y+1=e^x$ ......(i) From (i) and (ii), we obtain $\frac{x-y+1}{1-x+y}=e^{2 x} \Rightarrow(x-y+1)=(1-x+y) e^{2 x}$ |