4. \(\left(12x^3y^4z^2+6x^4y^3z-10x^2z\right):2x^2z=2x^2z\left(6xy^4z+3x^2y^3-5\right):2x^2z=6xy^4+3x^2y^3-5\)
5.\(=x^2-4-x^2-8x-16=-8x-20\)
6.\(=4x^2-x+4x-1-4x^2+3x=6x-1\)
7.\(=\left(m+n-m+n\right)\left(m+n+m-n\right)=2n.2m=4mn\)
8.\(=a^3+3a^2b+3ab^2+b^3-a^3+3a^2b-3ab^2+b^3=2b^3+6a^2b\)
9.\(=x^3-8+2\left(x^2-4\right)=x^3-8+2x^2-8=x^3+2x^2-16\)
10.\(=x^2-4x+4-x^2+3x+x-3=1\)