Ta có: 

M = 3xyz - 3x² + 5xy - 1

N = 5x² + xyz - 5xy + 3 - y

M + N = 3xyz - 3x² + 5xy - 1 + 5x² + xyz - 5xy + 3 - y

= -3x² + 5x² + 3xyz + xyz + 5xy - 5xy - y - 1 + 3

= 2x² + 4xyz - y +2.

M - N = (3xyz - 3x² + 5xy - 1) - (5x² + xyz - 5xy + 3 - y)

= 3xyz - 3x² + 5xy - 1 - 5x² - xyz + 5xy - 3 + y

= -3x² - 5x² + 3xyz - xyz + 5xy + 5xy + y - 1 - 3

= -8x² + 2xyz + 10xy + y - 4.

N - M = (5x² + xyz - 5xy + 3 - y) - (3xyz - 3x² + 5xy - 1)

= 5x² + xyz - 5xy + 3 - y - 3xyz + 3x² - 5xy + 1

= 5x² + 3x² + xyz - 3xyz - 5xy - 5xy - y + 3 + 1

= 8x² - 2xyz - 10xy - y + 4.

M = 3xyz - 3x² + 5xy - 1

N = 5x² + xyz - 5xy - 3 - y

M + N =  3xyz - 3x² + 5xy - 1 + 5x² + xyz - 5xy + 3 - y 

           = ( 3xyz + xyz ) + ( -3x² + 5x² ) + ( 5xy - 5xy ) + ( -1 + 3 ) - y

           = 4xyz + 2x² + 2 - y 

M+N

\(=3xyz-3x^2+5xy-1+5x^2+xyz-5xy+3\)

\(=2x^2+4xyz+2\)

M-N

\(=3xyz-3x^2+5xy-1-5x^2-xyz+5xy-3\)

\(=-8x^2+2xyz+10xy-4\)

M + N = (3xyz -3x²+5xy-1)+(5x²+xyz-5xy+3 - y)

          = 3xyz - 3x² +5xy-1+5x²+xyz-5xy+3 - y

         = (3xyz + xyz)+ (5x² - 3x²)+ (5xy-5xy)+(3-1)-y

          = 4xyz + 2x² + 2 - y 

M - N = (3xyz -3x²+5xy-1)-(5x²+xyz-5xy+3 - y)

          = 3xyz -3x²+5xy-1- 5x² -xyz+5xy-3 + y

          = (3xyz-xyz)+(-3x²-5x²)+(5xy+5xy)+(-1-3) + y

          = 2xyz + (-8x²)+10xy+(-4)+y

         =2xyz - 8x²+10xy - 4 +y

theo mk là zầy!!!!

a) M+N = 3xyz - 3x² + 5xy - 1 + 5x² + xyz - 5xy + 3 - y

            = (3xyz+xyz)+(-3x²+5x²)+(5xy-5xy)-y+(-1+3)

           =      4xyz    +      2x²      - y   + 2

duyệt đi

Phan Văn Hiếu câu b) là N-M mà bn???

duyệt đi

M + N = (3xyz – 3x2 + 5xy – 1) + (5x2 + xyz – 5xy + 3 – y)

      = 3xyz – 3x2 + 5xy – 1 + 5x2 + xyz – 5xy + 3 – y

      = (3xyz + xyz)+( –3x2 + 5x2) + (5xy – 5xy) – y + ( – 1+3)

      = 4xyz + 2x2 – y + 2

M – N = (3xyz – 3x2 + 5xy – 1) – (5x2 + xyz – 5xy + 3 – y)

      = 3xyz – 3x2 + 5xy – 1 – 5x2 – xyz + 5xy – 3 + y

      = (– 3x2 – 5x2) + (3xyz – xyz) + (5xy + 5xy) + y +(– 1 – 3)

      = –8x2 + 2xyz + 10xy + y – 4.

N – M = (5x2 + xyz – 5xy + 3 – y) – (3xyz – 3x2 + 5xy – 1)

      = 5x2 + xyz – 5xy + 3 – y – 3xyz + 3x2 – 5xy +1

      = (5x2 + 3x2)+ (xyz – 3xyz)+( – 5xy – 5xy) + (3 + 1 )– y

      = 8x2 – 2xyz – 10xy – y + 4.

Chú ý: Vì M – N và N – M là hai đa thức đối nhau nên

N – M = 8x2 – 2xyz – 10xy – y + 4

(Ta chỉ cần đổi dấu mỗi hạng tử của đa thức M – N là thu được N – M).

\(M+N=2x^2+4xyz-10xy+2-y\)

\(M-N=-8x^2+2xyz-4+y\)

\(N-M=8x^2-2xyz+4-y\)

đề bài là gì vậy bạn

 \(M + N = (3xyz – 3x^2 + 5xy – 1) + (5x^2 + xyz – 5xy + 3 – y)\)

      \(= 3xyz – 3x^2 + 5xy – 1 + 5x^2 + xyz – 5xy + 3 – y\)

      \(= (3xyz + xyz)+( –3x^2 + 5x^2) + (5xy – 5xy) – y + ( – 1+3)\)

      \(= 4xyz + 2x^2 – y + 2\)

 \(M – N = (3xyz – 3x^2 + 5xy – 1) – (5x^2 + xyz – 5xy + 3 – y)\)

      \(= 3xyz – 3x^2 + 5xy – 1 – 5x^2 – xyz + 5xy – 3 + y\)

      \(= (– 3x^2 – 5x^2) + (3xyz – xyz) + (5xy + 5xy) + y +(– 1 – 3)\)

      \(= –8x^2 + 2xyz + 10xy + y – 4.\)

\(N – M = (5x^2 + xyz – 5xy + 3 – y) – (3xyz – 3x^2 + 5xy – 1)\)

      \(= 5x^2 + xyz – 5xy + 3 – y – 3xyz + 3x^2 – 5xy +1\)

      \(= (5x^2 + 3x^2)+ (xyz – 3xyz)+( – 5xy – 5xy) + (3 + 1 )– y\)

      \(= 8x^2 – 2xyz – 10xy – y + 4.\)

M+N=(3xyz-3x³+5xy-1)+(5x²+xyz-5xy+3-y)

        =3xyz-3x³+5xy-1+5x²+xyz-5xy+3-y

        =(3xyz+xyz)+(-3x³)+(5xy-5xy)+(-1+3)+5x²-y

        =   4xyz+(-3x³)+2+5x²-y

M-N=(3xyz-3x³+5xy-1)-(5x²+xyz-5xy+3-y)

       =3xyz-3x³+5xy-1-5x²-xyz+5xy-3+y

       =(3xyz-xyz)+(-3x³)+(5xy+5xy)+(-1-3)-5x²+y

       =   2xyz+(-3x³)+10xy+(-4)-5x²+y

Mình làm tách riêng nha:

a) \(M+N\)

\(M+N=\left(3xyz-3x^2+5xy-1\right)+\left(5x^2+xyz-5xy+3-y\right)\)

\(M+N=\left(3xyz+xyz\right)+\left(-3x^2+5x^2\right)+\left(5xy-5xy\right)+\left(-1+3\right)-y\)

\(M+N=4xyz+2x^2+2-y\)

b) \(M-N\)

\(M-N=3xyz-3x^2+5xy-1-5x^2-xyz+5xy-3+y\)

\(=\left(3xyz-xyz\right)+\left(-3x^2-5x^2\right)+\left(5xy+5xy\right)+\left(-1-3\right)+y\)

\(=2xyz-8x^2+10xy-4+y\)

\(\)

M + N= 3xyz - 3x²+ 5xy - 1 + 5x² + xyz - 5xy+ 3 - y

= 3xyz + xyz - 3x² + 5x² + 5xy - 5xy - 1 + 3 - y

= 4xyz + 2x² + 2 - y

M - N= (3xyz - 3x² + 5xy - 1) - ( 5x² + xyz - 5xy + 3 - y)

= 3xyz - 3x² + 5xy -1 - 5x² - xyz + 5xy -3 + y

= 3xyz - xyz - 3x² - 5x² + 5xy + 5xy -1 - 3 + y

= 2xyz - 8x² + 10xy - 4 + y

N - M= (5x² + xyz - 5xy + 3 - y) - (3xyz - 3x²+ 5xy - 1)

= 5x² + xyz - 5xy + 3 - y - 3xyz + 3x² - 5xy + 1

= 5x² + 3x² + xyz - 3xyz - 5xy - 5xy + 3 + 1 - y

= 8x² - 2xyz - 10xy + 4 - y

Chúc bạn học tốt

Answer: