已知M=3x^2-2xy+y^2,N=2x^2+xy-3y^2,求M-N.

问题描述:

已知M=3x^2-2xy+y^2,N=2x^2+xy-3y^2,求M-N.

=3x²-2xy+y²-(2x²+xy-3y²)
=3x²-2xy+y²-2x²-xy+3y²
=x²-3xy+4y²