Đáp án:
A)
M=x2+y2+2xy2-6x2+3xy2
M=(x2-6x2)+y2+(2xy2+3xy2)
M=-5x2+y2+5xy2
b)
N=5xy+x2-7x2+2xy-4y2
N=(5xy+2xy)+x2+(-7x2-4y2)
=7xy+2x-11x2
C=(x2+x2)+(-2y2+y2)+xy-x2y2
=2x2-y2+xy-x2y2
C=x2+y2-x2y2-1-(x2-2y2+xy+1)
=x2+y2-x2y2-1-x2+2y2-xy-1
=(x2-x2)+(y2+2y2)-x2y2+(-1-1)-xy
=3y2-x2y2-2-xy