question_answer 1)

Form the differential equation of the family of circles having centre on Y-axis and radius 3 units. 

Answer:

Let (0, b) be the centre of members of gives family of circles.             where b is any parameter.       Differentiate it w.r.t. x, we get       2x + 2(y ? b)y? = 0             Put in equation (1)                   which is the required differential equation.