Question

cho mik hỏi với

Cho x-y=4 và x.y=5 tính B=x³ -y³+(x+y)²

Answer 1

\(B=x^3-y^3+\left(x+y\right)^2\)

\(=\left(x-y\right)^3+3xy\left(x-y\right)+\left(x-y\right)^2+4xy\)

\(=4^3+3\cdot4\cdot5+4^2+4\cdot5\)

\(=160\)

Answer 2

\(\left(x+y\right)^2=\left(x-y\right)^2+4xy=4^2+4.5=36\)

\(x^3-y^3=\left(x-y\right)^3+3xy\left(x-y\right)=4^3+3.5.4=124\)

\(\Rightarrow B=124+36=160\)