The equation of the family of parabolas with focus at the origin and x-axis as its axis is given by y2=4a(x+a) =4ax+4a2 ....(i) Differentiate the above expression 2y
dy
dx
=4a a=
1
2
y
dy
dx
....(ii) From cxpression (i) and (ii) y2=2xy
dy
dx
+y2(
dy
dx
)2 Here order =m=1 and =n=2 Now mn−m+n=1×2−1+2 =3