Consider the family of all circles whose centers lie on the straight line y = x. If this family of circles is represented by the differential equation Py" + Qy' +1=0, where P, Q are functions of x, y and y' (here y' dy/dx y'= d2y/dx2) then which of the following statements is (are) true?
(a) P = y + x
(b) P = y – x
(c) P + Q = 1 – x + y + y’ + (y’)2
(d) P – Q = x + y – y’ – (y’)2
