Bài 4:
b: \(B=\left(x-y\right)\left(x^2+xy+y^2\right)+2y^3-5-\left(x+y\right)\left(x^2-xy+y^2\right)\)
\(=x^3-y^3+2y^3-5-x^3-y^3\)
=-5
c: \(C=\left(x-1\right)^3-\left(x+1\right)^3-6\left(x+1\right)\left(x-1\right)\)
\(=x^3-3x^2+3x-1-x^3-3x^2-3x-1-6\left(x^2-1\right)\)
\(=-6x^2-2-6x^2+6\)
\(=-12x^2+4\)