Question 1085950
Use the discriminant b^2 - 4ac. 

a = 2, b = k, c = 6 

Set discriminant to 0 and solve for k. 

k^2 - 4(2)(6) = 0 

k^2 - 8(6) = 0 

k^2 - 48 = 0 

k^2 = 48 

sqrt{k^2} = sqrt{48} 

k = sqrt{16}•sqrt{3} 

k = 4•sqrt{3}, k = -4•sqrt{3} 

The negative k value is -4•sqrt{3}.