đề bài : rút gọn đa thức rồi cộng A = – 5x^3 + 6x^2 – 9x^3 – 7x^2 – x +12 B= -6x^3 – 7x^2 – 6x^2 – x^3 + 7x^2 – 12x -x

BÀI LÀM :

 $A$ $=$ $-5x^{3}$ + $6x^{2}$ – $9x^{3}$ – $7x^{2}$ – $x$ + $12$

$=$ ($-5x^{3}$- $9x^{3}$)+($6x^{2}$ – $7x^{2}$)+($-x$) + ($-12$) 

= $-14^3$ – $1x^2$ – $x$ + $12$

$B$ = $-6x^3$ – $7x^2$ – $6x^2$ – $x^3$ + $7x^2$ – $12x$ – $x$

= ( $-6x^3$ – $x^3$ ) + ( $-7x^2$ – $6x^2$ + $7x^2$ ) + (-12x – x)

= $-7x^3$ – $6x^2$ – $13x$

$*$

$A+B$ = ($-14x^3$ – $1x^2$ – x + 12 ) + ( $-7x^3$ – $6x^2$ – 13x )

= $ -14^3$ –  $1x^2$ – x + 12 – $7x^3$ – $6x^2$ – 13x

= $(-14x^3 – 7x^3)$ + $(-1x^2-6x^2)$ + (-x-13x) + (12)

= $-21x^3$ – $7x^2$ -14x +12

Chúc bạn học tốt :”)

#nocopy