\(x^2\left(x-2x^3\right)=x^3-2x^5\)
\(\left(x^2+1\right)\left(5-x\right)=5x^2-x^3+5-x\)
\(\left(x-2\right)\left(x^2+3x-4\right)=x^3+3x^2-4x-2x^2-6x+8=x^3+x^2-10x+8\)
\(\left(x+3\right)\left(x^2+3x-5\right)=x^3+3x^2-5x+3x^2+9x-15=x^3+6x^2+4x-15\)
\(\left(x^2-1\right)\left(x^2+2x\right)=x^4+2x^3-x^2-2x\)