Câu trả lời:

a/M+(5x²-2xy)=6x²+9xy-y²

=>M =(6x²+9xy-y²)-(5x²-2xy)=6x²+9xy-y²-5x²+2xy

=6x²-5x²+9xy+2xy-y²=x²+11xy-y²

b/M-(4xy-3y²)=x²-7xy+8y²

=>M=(x²-7xy+8y²)+(4xy-3y²)

=x²-7xy+8y²+4xy-3y²

=8y²-3y²-7xy+4xy+x²=5y²-3xy+x²