Explanation:
(C) : From question,
Equation of family of parabolas with focus
At, \((0,0)\) and \(\mathrm{x}\)-axis is-
\(y^{2}=4 k(x+k) \tag{i}\)
On differentiating both side w.r.t.x, we get-
\(2 \mathrm{y} \frac{\mathrm{dy}}{\mathrm{dx}}=4 \mathrm{k} \Rightarrow \mathrm{k}=\frac{\mathrm{y}}{2} \frac{\mathrm{dy}}{\mathrm{dx}}\)
Put, \(k=\frac{y}{2} \frac{d y}{d x}\) in equation (i), we get-
\(y^{2}=2 y \frac{d y}{d x}\left(x+\frac{y}{2} \frac{d y}{d x}\right) \Rightarrow y=2 x \frac{d y}{d x}+y\left(\frac{d y}{d x}\right)^{2}\)
Then, \(\quad \operatorname{order}(\mathrm{m})=1\), degree \((\mathrm{n})=2\)
So, \(\quad \mathrm{mn}-\mathrm{m}+\mathrm{n}=1 \times 2-1+2=3\)