Đáp án:
`x=2021`
Giải thích các bước giải:
`x+x/(1+2)+x/(1+2+3)+...+x/(1+2+3+...+4041)=4041`
`=>x*(1+1/(1+2)+1/(1+2+3)+...+1/(1+2+3+...+4041))=4041`
`=>`$x\cdot\left(1+\dfrac{1}{3}+\dfrac{1}{6}\ \!\! +\ \!\!.\!.\!.+\ \dfrac{1}{\dfrac{(4041+1).4041}{2}}\right)=4041$
`=>`$x\cdot\left(1+\dfrac{1}{3}+\dfrac{1}{6}\ \!\!+\ \!\!.\!.\!.+\ \dfrac{1}{\dfrac{4042.4041}{2}}\right)=4041$
`=>2x*(1/2+1/6+1/12+...+1/4041.4042)=4041`
`=>2x*(1/1.2+1/2.3+1/3.4+...+1/4041.4042)=4041`
`=>2x*(1-1/2+1/2-1/3+1/3-1/4+1/4+...+1/4041-1/4042)=4041`
`=>2x*(1-1/4042)=4041`
`=>2x*4041/4042=4041`
`=>2x=4041:4041/4042`
`=>2x=4042`
`=>x=4042:2`
`=>x=2021`
Vậy `x=2021`.
