Đáp án + Giải thích các bước giải:
`a)`
`A(x)+B(x)=4x^2+2x+5x^3-3+15+x^2+2x+5x^3`
`=(5x^3+5x^3)+(4x^2+x^2)+(2x+2x)-3+15`
`=10x^3+5x^2+4x+12`
$$$$
`b)`
`A(x)-B(x)=4x^2+2x+5x^3-3-(15+x^2+2x+5x^3)`
`=4x^2+2x+5x^3-3-15-x^2-2x-5x^3`
`=(5x^3-5x^3)+(4x^2-x^2)+(2x-2x)-3-15`
`=3x^2-18`
CHo `A(x)-B(x)=0`
`to 3x^2-18=0`
`to 3x^2=18`
`to x^2=6`
`to x=+-sqrt(6)`
$$$$
`c)`
`-B(x)=-D(x)-A(x)`
`to D(x)=-A(x)+B(x)`
`to D(x)=-(4x^2+2x+5x^3-3)+15+x^2+2x+5x^3`
`to D(x)=-4x^2-2x-5x^3+3+15+x^2+2x+5x^3`
`to D(x)=(5x^3-5x^3)+(x^2-4x^2)+(2x-2x)+3+15`
`to D(x)=-3x^2+18`