s1=x2+y2+2ax+cy+a=0s2=x2+y2−3ax+dy−1=0 Equation of common chord of circles s1 and s2 is given by s1−s2=0⇒5ax+(c−d)y+a+1=0 Given that 5x+by−a=0 passes through P and Q∴ The two equations should represent the same line ⇒1a=bc−d=−aa+1⇒a+1=−a2a2+a+1=0No real value of a.