For one and only 1 real solution, the discriminant = 0 (see chart attached) So we know b^2-4ac=0 when the equation is in the format of ax^2+bx-c=0. Make sure your equation is in the right format first!
Given kx^2+12x-4=0 b=12 so b^2-4ac=0 144 = 4ac 144 = 4(k)(-4) 144/(-16) = k k = -9
