`a)P(x) = -x^4 - 3x^3 + x^2 + 5x + 5`
`Q(x) = x^4 + 3x^3 - x^2 - 2x -2 `
`b) M(x) = P(x) + Q(x)`
`M(x)=(-x^4 - 3x^3 + x^2 + 5x + 5) + (x^4 + 3x^3 - x^2 - 2x - 2)`
`M(x)=-x^4-3x^3+x^2+5x+5+x^4+3x^3-x^2-2x-2`
`M(x)=(-x^4+x^4)+(-3x^3+3x^3)+(2x^2-2x^2)+(5x-2x)+(5-2)`
`M(x)=3x+3`
`N(x)=P(x)-Q(x)`
`N(x)=(-x^4-3x^3+x^2+5x+5)-(x^4+3x^3- x^2-2x-2)`
`N(x)=-x^4-3x^3+x^2+5x+5-x^4-3x^3+x^2+2x+2`
`N(x)=(-x^4-x^4)+(-3x^3-3x^3)+( x^2+x^2) +(5x+2x) +(5+2)`
`N(x)=-2x^4-6x^3+2x^2+7x+7`
`c)` Đặt M(x)=0 ta có : `3x+3=0`
`3x =0-3`
`3x =-3`
`x =-1`
Vậy nghiệm của `M(x)=3x+3` là `x=-1`
$\text{Xin hay nhất }$