Đáp án:
a,
`M=3,5x²y-2xy²+1,5x²y+2xy+3xy²`
` =(3,5x²y+1,5x²y)-(2xy²-3xy²)+2xy`
`=5x²y+xy²+2xy`
`N=2x²y+3,2xy+xy²-4xy²-1,2xy`
`=2x²y+(3,2xy-1,2xy)+(xy²-4xy²)`
`=2x²y+2xy-3xy²`
`b,M-N = 5x²y+xy²+2xy-(2x²y+2xy-3xy²)`
`= 5x²y+xy²+2xy-2x²y-2xy+3xy²`
`= (5x²y-2x²y)+(xy²+3xy²)+(2xy-2xy)`
`=3x²y+4xy²`
Giải thích các bước giải: