Đáp án:
2/ a/ $x=-\dfrac{6}{5}$
b/ $x=-3$
3/ a/ $x^4-1$
b/ $x^5+1$
Giải thích các bước giải:
2/ a/ $5(2x-1)-4(8x-3x)=7$
$⇔ 10x-5-20x=7$
$⇔ -10x=12$
$⇔ x=-\dfrac{12}{10}=-\dfrac{6}{5}$
b/ $7(2x-5)-5(7x-2)+2(5x-7)=(x-2)-(x+4)$
$⇔ 14x-35-35x+10+10x-14=x-2-x-4$
$⇔ -11x-39=-6$
$⇔ -11x=-6+39=33$
$⇔ x=\dfrac{33}{-11}=-3$
3/ a/ $(x-1)(x^3+x^2+x+1)$
$=(x-1)[x^2(x+1)+(x+1)]$
$=(x-1)(x+1)(x^2+1)$
$=(x^2-1)(x^2+1)$
$=x^4-1$
b/ $(x+1)(x^4-x^3+x^2-x+1)$
$=x^4(x+1)-x^3(x+1)+x^2(x+1)-x(x+1)+x+1$
$=x^5+x^4-x^4-x^3+x^3+x^2-x^2-x+x+1$
$=x^5+1$
