CGPET 2017 Solved Paper

Equation of circles having centre on Y-axis i.e. (0,a) (say) and radius 4 is
x2+(y−a)2=16........(i)
On differentiating w.r.t. x, we get
2x+2(y−a)

dy

dx

=0
⇒ (y−a)=−

x

dy dx

.......(ii)
On substituting the value of (y - a) in Eq. (i), we get
x2+(

−x

dy dx

)2=16
⇒x2(

dy

dx

)2+x2=16(

dy

dx

)2
⇒(x2−16)(

dy

dx

)2+x2=0