mn giúp mik câu 5 vs

`5.`

`a)`

`M+N=(3x^3 -x^2 y+2xy+3) + (x^2 y-2xy-2)`

`=3x^3 + (-x^2 y+x^2 y) + (2xy-2xy) + (3-2)`

`=3x^3 +1`

`b)`

`M-P=(3x^3 -x^2 y+2xy+3) - (3x^3 -2x^2 y-xy+3)`

`=(3x^3 -3x^3) + (-x^2 y+2x^2 y) + (2xy+xy) + (3-3)`

`=x^2 y+3xy`

`c)`

`M-2P = (3x^3 -x^2 y+2xy+3) - 2.(3x^3 -2x^2 y-xy+3)`

`=(3x^3 -x^2 y+2xy+3) + (-6x^3 + 4x^2 y+2xy-6)`

`=(3x^3 -6x^3) + (-x^2 y+4x^2 y) + (2xy+2xy) + (3-6)`

`=-3x^3 + 3x^2 y+4xy -3`

`d)`

`M+N+P = (3x^3 -x^2 y+2xy+3) + (x^2 y-2xy-2) + (3x^3 -2x^2 y-xy+3)`

`=(3x^3 +3x^3) + (-x^2 y+x^2 y-2x^2 y) + (2xy-2xy-xy) + (3-2+3)`

`=6x^3 -2x^2 y-xy+4`.