Ta có : \(S=\left(1-\frac{1}{2}\right)x\left(1-\frac{1}{3}\right)x\left(1-\frac{1}{4}\right)x...........x\left(1-\frac{1}{20}\right)\)
\(\Rightarrow S=\frac{1}{2}x\frac{2}{3}x\frac{3}{4}x.........x\frac{19}{20}\)
\(\Rightarrow S=\frac{1}{20}\)
Đúng nha !!!
a)\(||||x|+\frac{1}{3}|+\frac{1}{3}|+\frac{1}{3}|=1\)
b)\(|\frac{1}{2}x-\frac{2}{3}|-1=\frac{1}{6}\)
c)\(\frac{2}{6}+\frac{2}{12}+\frac{2}{20}+......+\frac{2}{x\left(x+1\right)}=\frac{4}{5}\)
Tìm x
làm giúp mih nha!!!!
Tìm số tự nhiên x, biết:
a, \(x-\frac{20}{11.13}-\frac{20}{13.15}-\frac{20}{15.17}-....-\frac{20}{53-55}=\frac{3}{11}\)
b, \(x+\frac{4}{5.9}+\frac{4}{9.13}+\frac{4}{13.17}+...+\frac{4}{41.45}=\frac{-37}{45}\)
c,\(\frac{1}{21}+\frac{1}{28}+\frac{1}{36}+\frac{2}{x\left(x+1\right)}=\frac{2}{9}\)
tìm x
a) \(\frac{x-1}{2}+\frac{x-2}{5}=\frac{1}{4}+\frac{x-7}{10}\)
b) \(3-\frac{2}{2x-3}=\frac{2}{5}+\frac{1}{2x-3}-\frac{3}{2}\)
c)\(7\cdot\left(x-1\right)+2x\cdot\left(1-x\right)=0\)
d) \(\frac{x+1}{2008}+\frac{x+2}{2017}+\frac{x+3}{2016}=\frac{x+10}{2009}+\frac{x+11}{2008}+\frac{x+12}{2007}\)
e) \(\frac{2}{\left(x-1\right)\cdot\left(x-3\right)}+\frac{5}{\left(x-3\right)\cdot\left(x-8\right)}+\frac{12}{\left(x-8\right)\cdot\left(x-20\right)}-\frac{1}{x-20}=\frac{-3}{4}\)
Tìm x:
\(a,\frac{2}{6}+\frac{2}{12}+\frac{2}{20}+...+\frac{2}{x\left(x+1\right)}=\frac{4}{5}\)
\(b,////x/+\frac{1}{3}/+\frac{1}{3}/+\frac{1}{3}/=1\)
Tìm x biết:
a,\(\frac{1}{2a^2+1}:x=2\)
b,\(x-\frac{20}{11.13}-\frac{20}{13.15}-\frac{20}{15.17}.........-\frac{20}{53.55}=\frac{3}{11}\)
c,\(\frac{1}{21}+\frac{1}{28}+\frac{1}{36}+........+\frac{2}{x\left(x+1\right)}=\frac{2}{9}\)
a) Tính
\(A=\left(1-\frac{1}{2}\right)\cdot\left(1-\frac{1}{3}\right)\cdot\left(1-\frac{1}{4}\right)\cdot\cdot\cdot\left(1-\frac{1}{2014}\right)\cdot\left(1-\frac{1}{2015}\right)\cdot\left(1-\frac{1}{2016}\right)\)
b) Tìm x:
\(\frac{x-2}{12}+\frac{x-2}{20}+\frac{x-2}{30}+\frac{x-2}{42}+\frac{x-2}{56}+\frac{x-2}{72}=\frac{16}{9}\)
Bài 1: Tìm x biết:
a. \(\frac{5}{1.6}+\frac{5}{6.11}+...+\frac{5}{\left(5x+1\right)\left(5x+6\right)}=\frac{2010}{2011}\)
b. \(\frac{7}{x}+\frac{4}{5.9}+\frac{4}{9.13}+\frac{4}{13.17}+..+\frac{4}{41.45}=\frac{29}{45}\)
c. \(1+\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+...+\frac{1}{x\left(x+2\right)}:2\)
d. (x-20) . \(\frac{\frac{1}{2}+\frac{1}{3}+..+\frac{1}{2000}}{\frac{1}{199}+\frac{2}{198}+\frac{3}{197}+...+\frac{198}{2}+\frac{199}{1}}=\frac{1}{2000}\)
Bài 2:
\(\frac{a}{n\left(n+a\right)}=\frac{1}{n}-\frac{1}{n+a}\left(n,a\right)\in Nsao\)
Bài 3:
a)\(\frac{3}{x}+\frac{y}{3}=\frac{5}{6}\)
b) \(\frac{x}{3}-\frac{4}{y}=\frac{1}{5}\)
c) \(\frac{x}{2}+\frac{y}{3}=\frac{x+y}{2+3}\)
d) \(\frac{x-1}{9}+\frac{1}{3}=\frac{1}{y+2}\)
Bài 1: Tìm x, biết:
\(\frac{1}{2.3}x+\frac{1}{3.4}x+\frac{1}{4.5}x+.....+\frac{1}{49.50}x=1\)
Bài 2: Chứng minh rằng:
\(a)A=1+\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{4^2}+.....+\frac{1}{100^2}< 2\)
\(b)B=1+\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+.....+\frac{1}{63}< 6\)
\(c)C=\frac{1}{2}.\frac{3}{4}.\frac{5}{6}.......\frac{9999}{10000}< \frac{1}{100}\)
Bài 3: Tính tổng:
\(S=\frac{1+2+2^2+2^3+.....+2^{2008}}{1-2^{2009}}\)
tìm x biết
a) 3x-\(\frac{1}{5}\)=\(\frac{4+x}{2}\)
b) \(\frac{4}{3}\)x-1=\(\frac{4\left(x+1\right)}{3}-\frac{1}{3}\)
c) 20% .x - \(1\frac{1}{4}=\frac{x+3}{2}\)
