`a) f(x)-g(x)+h(x) = (x^3-2x^2+3x+1)-(x^3+x+1)+(2x^2-1)`
`= x^3-2x^2+3x+1-x^3-x-1+2x^2-1`
`=(x^3-x^3)+(-2x^2+2x^2)+(3x-x)+(1-1-1)`
`=2x+(-1)`
`=2x-1.`
`b) Để f(x) - g(x) + h(x)=5 ⇔ 2x-1 =5 `
`⇔ 2x = 5+1`
`⇔ 2x = 6`
`⇔ x=6:2`
`⇔ x=3.`
Vậy `a) f(x)-g(x)+h(x)=2x-1.`
`b) f(x) - g(x) + h(x)=5 ⇔ x=3.`