Question

Answer 1

`3,`

`a,`

`A=-x^3-2x^2+4x^3-2x-1`

`= (-x^3+4x^3)-2x^2-2x-1`

`= 3x^3-2x^2-2x-1`

`B=2x^4-3x^3+x^2-2x^4+5x+3`

`= (2x^4-2x^4)-3x^3+x^2+5x+3`

`= -3x^3+x^2+5x+3`

`b,`

`A+B=(3x^3-2x^2-2x-1)+( -3x^3+x^2+5x+3)`

`= 3x^3-2x^2-2x-1-3x^3+x^2+5x+3`

`= (3x^3-3x^3)+(-2x^2+x^2)+(-2x+5x)+(-1+3)`

`= -x^2+3x+2`

`A-B=(3x^3-2x^2-2x-1)-( -3x^3+x^2+5x+3)`

`= 3x^3-2x^2-2x-1+3x^3-x^2-5x-3`

`= (3x^3+3x^3)+(-2x^2-x^2)+(-2x-5x)+(-1-3)`

`= 6x^3-3x^2-7x-4`

Answer 2

\(a,\)

\(A=-x^3-2x^2+4x^3-2x-1\)

\(=\left(-x^3+4x^3\right)-2x^2-2x-1\)

\(=3x^3-2x^2-2x-1\)

\(B=2x^4-3x^3+x^2-2x^4+5x+3\)

\(=\left(2x^4-2x^4\right)-3x^3+x^2+5x+3\)

\(=-3x^3+x^2+5x+3\)

\(b,A+B=3x^3-2x^2-2x-1-3x^3+x^2+5x+3\)

\(=\left(3x^3-3x^3\right)+\left(-2x^2+x^2\right)+\left(-2x+5x\right)+\left(-1+3\right)\)

\(=0+-x^2+3x+2\)

\(=-x^2+3x+2\)

\(A-B=\left(3x^3-2x^2-2x-1\right)-\left(-3x^3+x^2+5x+3\right)\)

\(=3x^3-2x^2-2x-1+3x^3-x^2-5x-3\)

\(=\left(3x^3+3x^3\right)+\left(-2x^2-x^2\right)+\left(-2x-5x\right)+\left(-1-3\right)\)

\(=6x^3-3x^2-7x-4\)

Answer 3

Lời giải:
a. 
$A=(-x^3+4x^3)-2x^2-2x-1=3x^3-2x^2-2x-1$
$B=(2x^4-2x^4)-3x^3+x^2+5x+3=-3x^3+x^2+5x+3$
b.

$A+B=(3x^3-2x^2-2x-1)+(-3x^3+x^2+5x+3)=-x^2+3x+2$

$A-B=(3x^3-2x^2-2x-1)-(-3x^3+x^2+5x+3)=6x^3-3x^2-7x-4$