Phân tích đa thức thành nhân tử: (x + y + z)^3 – x^3 – y^3 – z^3

(x+y+z)³− x³−y³−z³

= [(x + y) + z]³ – x³ – y³ – z³

= (x + y)³ + 3(x + y)²z + 3(x + y)z² + z³ – x³ – y³ – z³

= x³ + y³ + 3xy(x + y) + 3(x + y)²z + 3(x + y)z² – x³ – y³

(vì z³ – z³ = 0; 3x²y + 3xy² = 3xy(x + y))

= 3xy.(x + y) + 3(x + y)².z + 3(x + y).z²

= 3(x + y)[xy + (x + y)z + z²]

= 3(x + y)[xy + xz + yz + z²]

= 3(x + y)[x(y + z) + z(y + z)]

= 3(x + y)(y + z)(x + z)