Question

Hộ mình vs

 

Answer 1

\(A=-2\left(a^3+b^3\right)=-2\left[\left(a+b\right)^3-3ab\left(a+b\right)\right]\)

\(=-2.\left[\left(-2\right)^3-3\left(-8\right).\left(-2\right)\right]=112\)

Answer 2

\(A=-2a^3-2b^3=-2\left(a^3+b^3\right)\)

    \(=-2\left(a+b\right)\left(a^2-ab+b^2\right)\)

    \(=-2\left(a+b\right)\left(a^2+2ab+b^2-3ab\right)\)

    \(=-2\left(a+b\right)(\left(a+b\right)^2-3ab)\)

Thay \(a+b=-2\) và \(ab=-8\) ta đc:

 \(A=-2\cdot\left(-2\right).\left(\left(-2\right)^2-3\cdot\left(-8\right)\right)=112\)