1+1.1+1+1+1+1+1+111= 118

1+1.1+1+1+1+1+1+111=118

**** nha

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mé

đừng đăng linh tinh nx

(1-1/2)*(1-1/3)*(1-1/4)*...*(1-1/2018) 

= 1/2*2/3*3/4*...*2017/2018 

= 1/2018 

Đặt \(S=\left(1-\frac{1}{2}\right)\cdot\left(1-\frac{1}{3}\right)\cdot\left(1-\frac{1}{4}\right)\cdot\cdot\cdot\cdot\cdot\left(1-\frac{1}{2018}\right)\)

\(\Rightarrow S=\frac{1}{2}\cdot\frac{2}{3}\cdot\frac{3}{4}\cdot\cdot\cdot\cdot\cdot\frac{2017}{2018}\)

\(\Rightarrow S=\frac{1.2.3.....2017}{2.3.4.....2018}\)

\(\Rightarrow S=\frac{1}{2018}\)

\(\left(1+\frac{1}{2}\right)\left(1+\frac{1}{3}\right)..\left(1+\frac{1}{2019}\right)\)

\(=\frac{3}{2}\cdot\frac{4}{3}\cdot...\cdot\frac{2020}{2019}\)

\(=\frac{2020}{2}=1010\)

\(\left(1+\frac{1}{2}\right)\left(1+\frac{1}{3}\right)...\left(1+\frac{1}{2019}\right)\)

\(=\frac{3}{2}\cdot\frac{4}{3}\cdot...\cdot\frac{2020}{2019}\)

\(=\frac{2020}{2}\)

\(=1010\)

a) \(x=2\)

b) \(x=\frac{5}{36}\)

a) \(1-\left(\frac{2x}{3}+2\right)=-1\cdot\frac{1}{3}\)

\(1-\frac{2}{3}x-2=-\frac{1}{3}\)

\(-\frac{2}{3}x-1=-\frac{1}{3}\)

\(-\frac{2}{3}x=\frac{2}{3}\)

\(x=-1\)

----------------------------------------------------------

b) \(\frac{2}{5}x-1\cdot\frac{1}{2}x+x=\frac{1}{3}\)

\(\left(\frac{2}{5}-\frac{1}{2}+1\right)x=\frac{1}{3}\)

\(\frac{9}{10}x=\frac{1}{3}\)

\(x=\frac{1}{3}:\frac{9}{10}\)

\(x=\frac{10}{27}\)

\(\dfrac{1}{1.2}+\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+...+\dfrac{1}{x.\left(x+1\right)}=\dfrac{499}{500}\)

\(\Leftrightarrow1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{x}-\dfrac{1}{x+1}=\dfrac{499}{500}\)

\(\Leftrightarrow1-\dfrac{1}{x+1}=\dfrac{499}{500}\)

\(\Leftrightarrow x=499\)

giúp e vs

Đm mày nứng à

zzzz ko trả lời thì thôi chứ đừng chửi thề nhé