de cho 5/x-1 la so tu nhien 

thì x-1 là Ư của 5

* x-1=1

x=2

* x-1=5

x=4

thanks.

ai hỏi

quá hay

\(\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+...+\frac{2}{x.(x+1)}=\frac{2007}{2009}\)

=> \(2.\left(\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{x.\left(x+1\right)}\right)=\frac{2017}{2019}\)

=> \(2.\left(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{x.\left(x+1\right)}\right)=\frac{2017}{2019}\)

=> \(2.\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{x}-\frac{1}{x+1}\right)=\frac{2017}{2019}\)

=> \(2.\left(\frac{1}{2}-\frac{1}{x+1}\right)=\frac{2007}{2009}\)

=> \(\frac{1}{2}-\frac{1}{x+1}=\frac{2007}{2009}:2\)

=> \(\frac{1}{2}-\frac{1}{x+1}=\frac{2007}{4018}\)

=> \(\frac{1}{x+1}=\frac{1}{2}-\frac{2017}{4018}\)

=> \(\frac{1}{x+1}=\frac{1}{2019}\)

Vì 1 = 1

=> x + 1 = 2019

=> x       = 2019 - 1

=> x       = 2018

tra

r lời 

x=2018 

chúc bn 

hc tốt

A={ 0;1;2;3}

B={3;4}

C={0;4}

\(\frac{1}{3.5}+\frac{1}{5.7}+...+\frac{1}{x\left(x+2\right)}=\frac{11}{75}\)

\(\Leftrightarrow\frac{1}{2}\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{x}-\frac{1}{x+2}\right)=\frac{11}{75}\)

\(\Leftrightarrow\frac{1}{3}-\frac{1}{x+2}=\frac{11}{75}:\frac{1}{2}=\frac{22}{75}\Leftrightarrow\frac{1}{x+2}=\frac{1}{25}\Leftrightarrow x=23\)

=>0<x<6/12+4/12+3/12=13/12

hay x=1

có x=2k+1 => x là 1 số lẻ

nên M có 55 phân tử

tổng các phân tử là 4235

a: \(\frac23=\frac{x}{54}\)

=>\(\frac{x}{54}=\frac{2\cdot18}{3\cdot18}=\frac{36}{54}\)

=>x=36

b: \(\frac{10}{x}=\frac{15}{6}\)

=>\(\frac{10}{x}=\frac52\)

=>\(x=10\times\frac25=\frac{20}{5}=4\)

c: \(\frac23<\frac{x}{6}<1\)

=>\(\frac46<\frac{x}{6}<\frac66\)

=>4<x<6

mà x là số tự nhiên

nên x=5

d: Ta có: \(1<\frac{6}{x}<2\)

=>\(\frac66<\frac{6}{x}<\frac63\)

=>6>x>3

mà x là số tự nhiên

nên x∈{4;5}