Question

[Nghiêm Đình Quyền]

giải hộ mình với ạ!!!!!!!!!!!!!!!!!!!!!!!!!!

Answer 1

[missing you =]

bài 46:

a, \(x+y=2=>\left(x+y\right)^2=4\)\(=>x^2+y^2+2xy=4=>10+2xy=4\)

\(=>xy=\dfrac{4-10}{2}=-3\)

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

\(=\left(x+y\right)^3\)\(-3xy\left(x+y\right)=2^3-3.\left(-3\right).2=26\)

\(b,\) \(x+y=a=>x^2+2xy+y^2=a^2\)

\(=>xy=\dfrac{a^2-b}{2}\)

có: \(x^3+y^3=\left(x+y\right)^3-3xy\left(x+y\right)=a^3-3\left(\dfrac{a^2-b}{2}\right)a\)

\(=a^3-\dfrac{3a^3-3ab}{2}\)