$(x^2 - x + 1)(x^2 + ax + b) = x^4 + ax^3 + bx^2 - x^3 - ax^2 - bx + x^2 + ax + b = x^4 + (a-1)x^3 + (b-a+1)x^2 + (a-b)x + b$ - Portal da Acústica