If the roots of x2−bxax−c=K−1K+1   are numerically equal but opposite in sign, then K =

(x2−bx)(K+1)=(K−1)(ax−c) Roots are equal in magnitude but opposite in sign⇒ Coefficient of x =0⇒−b(K+1)−a(K−1)=0 ⇒K=a−ba+b