3x+x=4x, т.к. 3х=x+x+x.
x+x+x+x=4x
x² + px + q
x₁ = - 10 x₂ = - 18
q = x₁ * x₂ = - 10 * (- 18) = 180
- p = - 10 + (- 18) = - 28
x² + 28x + 180 = 0