Bài `2:`

`P(x)+Q(x)`

`=4x^3 +3x^2 +2x+7 -4x^3 -2x^2 +4x-7`

`=(4x^3-4x^3)+(3x^2-2x^2)+(2x+4x)+(7-7)`

`=x^2+6x`

`P(x)-Q(x)`

`=4x^3+3x^2+2x+7-(-4x^3-2x^2+4x-7)`

`=4x^3+3x^2+2x+7+4x^3+2x^2-4x+7`

`=8x^3+5x^2-2x+14`

Bài `3:`

`a, A(x)=4x^4 -2x^3 -2x^4 +7x^3 +3x-1/4-x+1/3`

`=2x^4 +5x^3 +2x+1/12`

Bậc `:4`

`B(x)=x^4 +x^3 +2x^2-x^4 +3x^3 -x^2-2x+1/12`

`=4x^3 +x^2 -2x+1/12`

Bậc `:3`

`b,` `M(x)=A(x)+B(x)`

`=2x^4 +5x^3 +2x+1/12 + 4x^3 +x^2 -2x+1/12`

`=2x^4 +9x^3 +x^2 +1/6`

`N(x)=A(x)-B(x)`

`=2x^4 +5x^3 +2x+1/12 -( 4x^3 +x^2 -2x+1/12)`

`=2x^4 +5x^3 +2x+1/12 - 4x^3 -x^2+2x-1/12`

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