Tìm x
a. \(x-\dfrac{20}{11.13}-\dfrac{20}{13.15}-\dfrac{20}{15.17}-...-\dfrac{20}{53.55}\)
b. \(\dfrac{1}{21}+\dfrac{1}{28}+\dfrac{1}{36}+...+\dfrac{2}{x\left(x+1\right)}=\dfrac{2}{9}\)
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Tìm x :
a. \(x-\dfrac{20}{11.13}-\dfrac{20}{13.15}-\dfrac{20}{15.17}-....-\dfrac{20}{53.55}\)
b. \(\dfrac{1}{21}+\dfrac{1}{28}+\dfrac{1}{36}+...+\dfrac{2}{x\left(x+1\right)}=\dfrac{2}{9}\)
Chứng minh \(⋮\) 31
Tìm x biết:
a) \(\dfrac{x+5}{3}\)=\(\dfrac{x-6}{7}\)
b) x - \(\dfrac{20}{11.13}\)-\(\dfrac{20}{13.15}\)-\(\dfrac{20}{15.17}\)-...-\(\dfrac{20}{53.55}\)=\(\dfrac{3}{11}\)
\(\dfrac{1}{3}\)+\(\dfrac{1}{6}\)+\(\dfrac{1}{10}\)+...+\(\dfrac{2}{n\left(n+1\right)}\)=\(\dfrac{2015}{2016}\)
a) Vì \(\dfrac{x+5}{3}\)= \(\dfrac{x-6}{7}\) nên 7(x+5) = 3(x-6)
=> 7x+ 35 = 3x - 18
7x - 3x = -18 -35
4x = -53
x = -53:4
x = \(\dfrac{-53}{4}\)
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x-\(\dfrac{20}{11.13}-\dfrac{20}{13.15}-\dfrac{20}{15.17}-...-\dfrac{20}{53.55}=\dfrac{3}{11}\)
A=\(\dfrac{1}{1.2}+\dfrac{1}{2.3}+...+\dfrac{1}{99.100}\)
\(\dfrac{-2}{3}\left|x\right|+1\dfrac{1}{2}=\dfrac{2}{5}\)
các bạn phại đổi kiểu chữ để làm bài này (VNI) , (TELEX)
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x - \(\dfrac{20}{11.13}-\dfrac{20}{13.15}-\dfrac{20}{15.17}-........-\dfrac{20}{53.55}=\dfrac{3}{11}\)
x - \(\left(\dfrac{20}{11.13}+\dfrac{20}{13.15}+\dfrac{20}{15.17}+...+\dfrac{20}{53.55}\right)=\dfrac{3}{11}\)
Đặt A = \(\dfrac{20}{11.13}+\dfrac{20}{13.15}+\dfrac{20}{15.17}+...+\dfrac{20}{53.55}\)
A = \(\dfrac{20}{2}\left(\dfrac{2}{11.13}+\dfrac{2}{13.15}+\dfrac{2}{15.17}+....+\dfrac{2}{53.55}\right)\)
A = \(\dfrac{20}{2}\left(\dfrac{1}{11}-\dfrac{1}{13}+\dfrac{1}{13}-\dfrac{1}{15}+\dfrac{1}{15}-\dfrac{1}{17}+...+\dfrac{1}{53}-\dfrac{1}{55}\right)\)
A = \(10.\left(\dfrac{1}{11}-\dfrac{1}{55}\right)\)
A = 10 . 4/55
A = 8/11
TA Có : x - 8/11 = 3/11
x = 3/11 + 8/11
x = 11/11
x = 1
Vậy x = 1
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Tìm x :
\(\dfrac{0,2}{\left|2x-1\right|}-\dfrac{20}{11.13}-\dfrac{20}{13.15}-\dfrac{20}{15.17}-...-\dfrac{20}{53.55}=\dfrac{3}{11}\)
Tìm x, biết:
a).left(dfrac{1}{1.101}+dfrac{1}{2.102}+...+dfrac{1}{10.110}right).xdfrac{1}{1.11}+dfrac{1}{2.12}+...+dfrac{1}{100.110}
b).x-dfrac{20}{11.13}-dfrac{20}{13.15}-dfrac{20}{15.17}-...-dfrac{20}{53.55}dfrac{3}{11}
c).dfrac{x-1}{99}+dfrac{x-2}{98}+dfrac{x-5}{95}3+dfrac{1}{99}+dfrac{1}{98}+dfrac{1}{95}
Mấy bạn tính nhanh, hợp lí, giải ra từng bước dùm mik nha
Thanks m.n
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Tìm x, biết:
a).\(\left(\dfrac{1}{1.101}+\dfrac{1}{2.102}+...+\dfrac{1}{10.110}\right).x=\dfrac{1}{1.11}+\dfrac{1}{2.12}+...+\dfrac{1}{100.110}\)
b).\(x-\dfrac{20}{11.13}-\dfrac{20}{13.15}-\dfrac{20}{15.17}-...-\dfrac{20}{53.55}=\dfrac{3}{11}\)
c).\(\dfrac{x-1}{99}+\dfrac{x-2}{98}+\dfrac{x-5}{95}=3+\dfrac{1}{99}+\dfrac{1}{98}+\dfrac{1}{95}\)
Mấy bạn tính nhanh, hợp lí, giải ra từng bước dùm mik nha
Thanks m.n
b: \(\Leftrightarrow x-10\left(\dfrac{2}{11\cdot13}+\dfrac{2}{13\cdot15}+...+\dfrac{2}{53\cdot55}\right)=\dfrac{3}{11}\)
\(\Leftrightarrow x-10\left(\dfrac{1}{11}-\dfrac{1}{13}+\dfrac{1}{13}-\dfrac{1}{15}+...+\dfrac{1}{53}-\dfrac{1}{55}\right)=\dfrac{3}{11}\)
\(\Leftrightarrow x-10\cdot\dfrac{4}{55}=\dfrac{3}{11}\)
=>x=3/11+20/55=3/11+4/11=7/11
c: \(\Leftrightarrow\left(\dfrac{x-1}{99}-1\right)+\left(\dfrac{x-2}{98}-1\right)+\left(\dfrac{x-5}{95}-1\right)=\dfrac{1}{99}+\dfrac{1}{98}+\dfrac{1}{95}\)
\(\Leftrightarrow x-100=1\)
hay x=101
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tìm x thuộc N
\(x-\dfrac{20}{11.13}-\dfrac{20}{13.15}-\dfrac{20}{15.17}-...-\dfrac{20}{53.55}=\dfrac{3}{11}\)
\(x-\dfrac{20}{11.13}-\dfrac{20}{13.15}-\dfrac{20}{15.17}-...-\dfrac{20}{53.55}=\dfrac{3}{11}\)
\(x-10\left(\dfrac{2}{11.13}+\dfrac{2}{13.15}+\dfrac{2}{15.17}+...+\dfrac{2}{53.55}\right)=\dfrac{3}{11}\)
\(x-10\left(\dfrac{1}{11}-\dfrac{1}{13}+\dfrac{1}{13}-\dfrac{1}{15}+\dfrac{1}{15}-\dfrac{1}{17}+...+\dfrac{1}{53}-\dfrac{1}{55}\right)=\dfrac{3}{11}\)
\(x-10\left(\dfrac{1}{11}-\dfrac{1}{55}\right)=\dfrac{3}{11}\)
\(x-10.\dfrac{4}{55}=\dfrac{3}{11}\)
\(x-\dfrac{8}{11}=\dfrac{3}{11}\)
\(x=\dfrac{3}{11}+\dfrac{8}{11}=1\)
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text{Tìm x, biết:}a) x-dfrac{2}{3.5}-dfrac{2}{5.7}-dfrac{2}{7.9}-dfrac{2}{9.11}-dfrac{2}{11.13}-dfrac{2}{13.15}dfrac{2}{5}b) dfrac{1}{2.3}.x+dfrac{1}{3.4}.x+dfrac{1}{4.5}.x+...+dfrac{1}{49.50}.x1c) x-dfrac{20}{11.3}-dfrac{20}{13.15}-...-dfrac{53}{55}dfrac{3}{11}d) x+dfrac{4}{5.9}+dfrac{4}{9.13}+...+dfrac{4}{41.45}dfrac{-37}{45}e) left(dfrac{11}{12}.dfrac{11}{2.23}.dfrac{11}{23.34}...dfrac{11}{89.100}right).xdfrac{5}{3}f) left(dfrac{2}{11.13}.dfrac{2}{13.15}.dfrac{2}{15.17}...dfrac{2}{19.21}right...
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\(\text{Tìm x, biết:}\)
\(a\)) \(x-\dfrac{2}{3.5}-\dfrac{2}{5.7}-\dfrac{2}{7.9}-\dfrac{2}{9.11}-\dfrac{2}{11.13}-\dfrac{2}{13.15}=\dfrac{2}{5}\)
\(b\)) \(\dfrac{1}{2.3}.x+\dfrac{1}{3.4}.x+\dfrac{1}{4.5}.x+...+\dfrac{1}{49.50}.x=1\)
\(c\)) \(x-\dfrac{20}{11.3}-\dfrac{20}{13.15}-...-\dfrac{53}{55}=\dfrac{3}{11}\)
\(d\)) \(x+\dfrac{4}{5.9}+\dfrac{4}{9.13}+...+\dfrac{4}{41.45}=\dfrac{-37}{45}\)
\(e\)) \(\left(\dfrac{11}{12}.\dfrac{11}{2.23}.\dfrac{11}{23.34}...\dfrac{11}{89.100}\right).x=\dfrac{5}{3}\)
\(f\)) \(\left(\dfrac{2}{11.13}.\dfrac{2}{13.15}.\dfrac{2}{15.17}...\dfrac{2}{19.21}\right)-x+4+\dfrac{221}{231}=\dfrac{7}{3}\)
d) Ta có: \(x+\dfrac{4}{5\cdot9}+\dfrac{4}{9\cdot13}+...+\dfrac{4}{41\cdot45}=\dfrac{-37}{45}\)
\(\Leftrightarrow x+\dfrac{1}{5}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{13}+...+\dfrac{1}{41}-\dfrac{1}{45}=\dfrac{-37}{45}\)
\(\Leftrightarrow x+\dfrac{1}{5}-\dfrac{1}{45}=\dfrac{-37}{45}\)
\(\Leftrightarrow x=\dfrac{-37}{45}+\dfrac{1}{45}-\dfrac{1}{5}=\dfrac{-36}{45}-\dfrac{1}{5}=\dfrac{-4}{5}-\dfrac{1}{5}=-1\)
Vậy: x=-1
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Tìm x biết
a, ( x + 1 ) + ( x + 4 ) + ( x + 7 ) + ... + ( x + 28 ) 155
b, 1 + dfrac{1}{3} + dfrac{1}{6} + dfrac{1}{10} + ..... + dfrac{2}{x+left(x+1right)} 1dfrac{2009}{2010}
c, left(dfrac{2}{11.13}+dfrac{2}{13.15}+dfrac{2}{15.17}+.....+dfrac{2}{19.21}right) . 462 - x 19
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Tìm x biết
a, ( x + 1 ) + ( x + 4 ) + ( x + 7 ) + ... + ( x + 28 ) = 155
b, 1 + \(\dfrac{1}{3}\) + \(\dfrac{1}{6}\) + \(\dfrac{1}{10}\) + ..... + \(\dfrac{2}{x+\left(x+1\right)}\) = \(1\dfrac{2009}{2010}\)
c, \(\left(\dfrac{2}{11.13}+\dfrac{2}{13.15}+\dfrac{2}{15.17}+.....+\dfrac{2}{19.21}\right)\) . 462 - x = 19
a, (x + 1) + (x + 4) + ... + (x + 28) = 155
x + 1 + x + 4 + ... + x + 28 = 155
(x + x + x + ... + x) + (1 + 4 + ... + 28) = 155
x . 10 + 145 = 155
x . 10 = 155 - 145
x . 10 = 10
x = 10 : 10
x = 1
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Tìm x, biết:
a) \(\left(3\dfrac{1}{2}-2.x\right).3\dfrac{1}{3}=7\dfrac{1}{3}\)
b) \(\dfrac{4}{9}.x=\dfrac{9}{8}-0,125\)
c) \(\dfrac{-X}{21}=\dfrac{20}{7}\)
a, \(\left(\dfrac{7}{2}-2x\right).\dfrac{10}{3}=\dfrac{22}{3}\Leftrightarrow\dfrac{7}{2}-2x=\dfrac{22}{10}=\dfrac{11}{5}\)
\(\Leftrightarrow2x=\dfrac{13}{10}\Leftrightarrow x=\dfrac{13}{20}\)
b, \(\dfrac{4x}{9}=\dfrac{9}{8}-\dfrac{125}{1000}=1\Leftrightarrow x=\dfrac{9}{4}\)
c, \(-\dfrac{x}{21}=\dfrac{60}{21}\Rightarrow x=-60\)
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