Question

Cho x-y=-3 xy=10. Tính a. x^2- 2xy + y^2 -1 b. x^2+y^2

Answer 1

a ) \(x^2-2xy+y^2-1\)

\(=\left(x-y\right)^2-1\)

\(=\left(-3\right)^2-1\)

\(=9-1\)

\(=8\)

b ) \(x^2+y^2\)

\(=x^2-20+y^2+20\)

\(=x^2-2.10+y^2+20\)

\(=x^2-2xy+y^2+20\)

\(=\left(x-y\right)^2+20\)

\(=\left(-3\right)^2+20\)

\(=29\)

Answer 2

a) \(x^2-2xy+y^2=\left(x-y\right)^2=\left(-3\right)^2=9\)

b) Có: \(x^2-2xy+y^2=9\)

=> \(x^2+y^2=9+2xy=9+2\cdot10=9+20=29\)