`f(x) = 0`
`\to x(x-3)+(x+3)^2=0`
`\to x^2 - 3x + x^2 + 6x + 9 = 0`
`\to 2x^2 + 3x + 9 =0`
`\to 2x^2 + 3x = -9`
`\to x^2 + 3/2x = -9/2`
`\to x^2 + 3/2 + (3/4)^2 = -9/2 + (3/4)^2`
`\to x^2 + 3/2x + 9/16 = -63/16`
`\to x^2 + 2*x*3/4 + (3/4)^2 = -63/16`
`\to (x+3/4)^2 = -63/16`
`\to |x+3/4| = sqrt{-63/16}` (vô lý)
Vậy pt vô nghiệm : `S = \emptyset`