Given, equations are x2+ax+b=0 ...(i) x2+bx+a=0 ...(ii) Let α be common root of Eqs. (i) and (ii), then α2+aα+b=0 ...(iii) α2+bα+a=0 ...(iv) Compare Eqs. (iii) and (iv), we get α2+aα+b=α2+bα+a ⇒α(a−b)=(a−b) ⇒α=1 Common root =1 From Eq. (iii), we get 1+a+b=0 ⇒a+b=−1