Question

cho x-y=2 Tính A=2(x^3-y^3)-3(x+y)^3

Answer 1

\(A=2\left(x^3-y^3\right)-3\left(x+y\right)^3\\ \Rightarrow A=2\left(x-y\right)\left(x^2+xy-y^2\right)-3\left(x^3+3x^2y+3xy^2+y^3\right)\\ \Rightarrow A=2.2\left(x^2+xy-y^2\right)-3x^3-9x^2y-9xy^2-3y^3\\ \Rightarrow A=4x^2+4xy-4y^2-3x^3-9x^2y-9xy^2-3y^3\)