Question

Rút gọn biểu thức

\(\left(x+1\right)^3+\left(x-1\right)^3+x^3-3x\left(x+1\right)\left(x-1\right)\)

Answer 1

\(\left(x+1\right)^3+\left(x-1\right)^3+x^3-3x\left(x+1\right)\left(x-1\right)\)

\(=x^3+3x^2+3x+1+x^3-3x^2+3x-1+x^3-3x\left(x^2-1\right)\)

\(=3x^3+6x-3x^4+3x\)

\(=-3x^4+3x^3+9x\)

Answer 2

\(x^3+3x^2y+3xy^2+y^3\)  \(+x^3-3x^2y+3xy^2-y^3\)\(+x^3-3x\left(x^2-1\right)\)

\(=3x^3+6xy^2-3x^3+3x\)

\(=3x\left(1+2y^2\right)\)