Question

phân tích đa thức thành nhân tử : \(\left(x+y+z\right)^3-x^3-y^3-z^3\)

Answer 1

\(\left(x+y+z\right)^3-x^3-y^3-z^3=\left[\left(x+y+z\right)^3-x^3\right]-\left(y^3+z^3\right)\)

Áp dụng các hằng đẳng thức

\(=\left(x+y+z-x\right)\left[\left(x+y+z\right)^2+\left(x+y+z\right)x+x^2\right]-\left(y+z\right)\left(y^2-yz+z^2\right)\)

\(=\left(y+z\right)\left[x^2+y^2+z^2+2xy+2xz+2yz+xy+xz+x^2+x^2-y^2+yz-z^2\right]\)

\(=\left(y+z\right)\left(3x^2+3xy+3xz+3yz\right)=3\left(y+z\right)\left[x\left(x+y\right)+z\left(x+y\right)\right]\)\(=3\left(x+y\right)\left(y+z\right)\left(x+z\right)\)