Tính A(x)+B(x) và A(x)-B(x) .

* Hướng dẫn giải

$A\left(x\right)+B\left(x\right)$
$=\left(x^6+5x^5+2x^4+x^3+2x^2-x+3\right)+\left(-x^6-4x^5+2x^3+3x^2+2x-12\right)$
$=x^5+2x^4+3x^3+5x^2+x-9$
$A\left(x\right)-B\left(x\right)=\left(x^6+5x^5+2x^4+x^3+2x^2-x+3\right)-\left(-x^6-4x^5+2x^3+3x^2+2x-12\right)$

$=2x^6+9x^5+2x^4-x^3-x^2-3x+15$