Consider the family of all eircles whose centres lie on the straight line yx, if this family of circles is represented by the differential equation py +oy+1-0,

Consider the family of all eircles whose centres lie on the straight line yx, if this family of circles is represented by the differential equation Py +Oy+1-0, where P, O are functions of x, y and y, then which of the following statements is/ are true? (a) P=y+x (6) P=y-x () P+0=1-x+y+y+0 (d) P-0-x+y-y-O