Question

Tìm đa thức M,N biết 

a , M + ( 5x²-2xy ) = 6x² + 9xy - y²

b, ( 3xy - 4y²) - N = x² - 7xy + 8y²

Answer 1

a) Ta có: \(M+\left(5x^2-2xy\right)=6x^2+9xy-y^2\)

\(\Leftrightarrow M=6x^2+9xy-y^2-5x^2+2xy\)

\(\Leftrightarrow M=x^2+11xy-y^2\)

Vậy: \(M=x^2+11xy-y^2\)

Answer 2

b) Ta có: \(\left(3xy-4y^2\right)-N=x^2-7xy+8y^2\)

\(\Leftrightarrow N=3xy-4y^2-x^2+7xy-8y^2\)

\(\Leftrightarrow N=-x^2+10xy-12y^2\)

Vậy: \(N=-x^2+10xy-12y^2\)