Bài 3 :
Ta có :$ x+ \frac{1}{2020} + x + \frac{2}{2020} + ...+ x+ \frac{2019}{2020}= 2020.x$
$⇔2019x + \frac{1}{2020}.(1+2+3+...+2019 ) = 2020x$
$⇔x= \frac{1}{2020}. \frac{2019.2020}{2}$
$⇔x= \frac{2019}{2}$
Vậy : $x= \frac{2019}{2}$
Chúc bạn học tốt !