x+2ay+a=0...(i) x+3by+b=0...(ii) x+4ay+a=0...(iii) Subtracting equation (iii) from (i) −2ay=0 ay=0=y=0 Putting value of y in equation (i), we get x+0+a=0 x=−a Putting value of x and y in equation (ii), we get −a+b=0⇒a=b Thus, (a,b) lies on a straight line