From differential equation representing the family of lines making equal intercepts on the co-ordinate axes.

Differential equation representing the curve : y=cos x is :

Form the differential equation representing the family of ellipses having foci on x-axis and centre at the origin.

Form the differential equation of the family of circles in the first quadrant which touch the coordinate axes.

Form the differential equation of the family of circles in the second quadrant and touching the coordinate axes.