Complete the square and solve the equation x^2+3x+...=0 Solution x^2+3x= 0 To complete the square and solve for x. We add (3/2)^2 to both sides so that x+3x+(3/2)^2 becomes a perfect square. x^2+3x+(3/2)^2 = (3/2)^2. (x+3/2)^2 = (3/2)^2. We take the square root: (x+3/2) = +3/2, x +3/2 = -3/2 x+3/2 = 3/2 gives x= 0. x+3/2 = -3/2 gives x= -3/2-3/2 = -3. So x= 0, or x= -3..