Question

For what values of k the roots of equation x2+4x+k=0 are real

Answer 1

Ans:-Let "m" be the common root of the given equation

              m^2 - 4m + k = 0...................(1)

         m^2 - km -4 = 0..........................(2)

          subtracting   (2)  from  (1), we get,

         m^2 - 4m +k -(m^2-km-4) = 0

           (-4-k)m +k+4=0

              (-4-k)m=-k-4

                  m=1

        Put in the equation x^2-4x+k=0

                         1-4+k=0

                            k=3