If `(x-a)costheta+ysintheta=(x-a)cosphi+ysinphi=a` and `tan(theta/2)-tan(phi/2)=2b` ,then (a) `y^2=2a x-(1-b^2)x^2` (b)`tan(theta/2)=1/x(y+b x)` (c)`y^2=2b x-(1-a^2)x^2` (d)`tan(phi/2)=1/x(y-b x)`