Determine the sum of all values of for which the following equation in has 2 equal roots:
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k x 2 + 2 x 2 − 3 k x + k = 0
( k + 2 ) x 2 − 3 k x + k = 0 ⟹ It is a quadratic equation in the form of a x 2 + b x + c = 0
So, a = k + 2 , b = − 3 k and c = k
So that the roots are equal, the discriminant must be equal to 0 . That is, b 2 − 4 a c = 0
So, we have
( − 3 k ) 2 − 4 ( k + 2 ) ( k ) = 0 ⟹ 9 k 2 − 4 k ( k + 2 ) = 0 ⟹ 9 k 2 − 4 k 2 − 8 k = 0 ⟹ 5 k 2 − 8 k = 0 ⟹ k ( 5 k − 8 ) = 0
k = 0
5 k − 8 = 0 ⟹ 5 k = 8 ⟹ k = 5 8
Finally,
0 + 5 8 = 1 . 6