Giải thích các bước giải:
$\text{Bài 2:}$
$a) 5(2x-1)-4(8x-3x)=7$
$⇔10x-5-4.5x=7$
$⇔10x-5-20x=7$
$⇔-10x=12$
$⇔x=-\dfrac{12}{10}=-\dfrac{6}{5}$
$\text{Vậy $x=-\dfrac{6}{5}$}$
$b)7(2x-5)-5(7x-2)+2(5x-7)=(x-2)-(x+4)$
$⇔14x-35-35x+10+10x-14=x-2-x-4$
$⇔-11x-39=-6$
$⇔-11x=39-6$
$⇔-11x=33$
$⇔x=-3$
$\text{ Vậy $x=-3$}$
$\text{Bài 3:}$
$a) (x-1)(x^3+x^2+x+1)$
$=x(x^3+x^2+x+1)-(x^3+x^2+x+1)$
$=x^4+x^3+x^2+x-x^3-x^2-x-1$
$=x^4-1+(x^3-x^3)+(x^2-x^2)+(x-x)$
$=x^4-1$
$a) (x+1)(x^4-x^3+x^2-x+1)$
$=x(x^4-x^3+x^2-x+1)+(x^4-x^3+x^2-x+1)$
$=x^5-x^4+x^3-x^2+x+x^4-x^3+x^2-x+1$
$=x^5+1+(-x^4+x^4)+(x^3-x^3)+(-x^2+x^2)+(x-x)$
$=x^5+1$
Học tốt!!!
