`a)f(x)=-x^5-7x^4-2x^3+x^2+4x+9`
`g(x)=x^5+7x^4+2x^3+2x^2-3x-9`
`b)h(x)=f(x)+g(x)`
`h(x)=(-x^5-7x^4-2x^3+x^2+4x+9)+(x^5+7x^4+2x^3+2x^2-3x-9)`
`=-x^5-7x^4-2x^3+x^2+4x+9+x^5+7x^4+2x^3+2x^2-3x-9`
`=(-x^5+x^5)+(-7x^4+7x^4)+(-2x^3+2x^3)+(x^2+2x^2)+(4x-3x)+(9-9)`
`=3x^2+x`
`k(x)=f(x)-g(x)`
`k(x)=(-x^5-7x^4-2x^3+x^2+4x+9)-(x^5+7x^4+2x^3+2x^2-3x-9)`
`k(x)=-x^5-7x^4-2x^3+x^2+4x+9-x^5-7x^4-2x^3-2x^2+3x+9`
`k(x)=(-x^5-x^5)+(-7x^4-7x^4)+(-2x^3-2x^3)+(x^2-2x^2)+(4x+3x)+(9+9)`
`k(x)=-2x^5-14x^4-4x^3-3x^2+7x+18`
`c)` Đặt `h(x)=0` ta có :`3x^2+x=0`
`3x.x+x=0`
`x.(3x+1)=0`
`=>x=0` hoặc `3x+1=0`
`3x=-1`
`x=-1/3`
Vậy nghiệm của `h(x)` là: `x∈{-1/3;0}`
$\text{Xin hay nhất}$
