3) is
2
2
2
2
x
y
a
+b
 = 1 (1)
Differentiating equation (1) with respect to x, we get 
2
2
2
2
0
x
y dy
dx
a
+b
=
or
y
dy
x
⎛dx
⎞
⎜
⎟
⎝
⎠ =
2
−ab2 (2)
Differentiating both sides of equation (2) with respect to x, we get
2
2
2
xdy
y
y
d y
dy
dx
x
dx
dx
x
 
 
 
 
 
 
 
 
 
 
 
  
 
 
 
 
  
 
 
 
 = 0
or
2
2
2
–
d y
dy
dy
xy
x
y
dx
dx
dx
 
 
 
 
 
 
 
 = 0 (3)
which is the required differential equation