Đáp án:
Giải thích các bước giải:
`P(x)=3x^3-7x^2+x+7`
`Q(x)=7x^3-7x^2+2x+5`
`P(x)+Q(x)=3x^3-7x^2+x+7+(7x^3-7x^2+2x+5)`
`P(x)+Q(x)=3x^3-7x^2+x+7+7x^3-7x^2+2x+5`
`P(x)+Q(x)=3x^3+7x^3-7x^2-7x^2+x+2x+7+5`
`P(x)+Q(x)=10x^3-14x^2+3x+12`
`P(x)+Q(x)=3x^3-7x^2+x+7-(7x^3-7x^2+2x+5)`
`P(x)+Q(x)=3x^3-7x^2+x+7-7x^3+7x^2-2x-5`
`P(x)+Q(x)=3x^3-7x^3-7x^2+7x^2+x-2x+7-5`
`P(x)+Q(x)=-4x^3-x+2`
