\(\dfrac{1}{9}\)+\(\dfrac{1}{18}\)+\(\dfrac{1}{30}\)+...+\(\dfrac{1}{135}\)
Tính nhanh
K
Khách
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Những câu hỏi liên quan
16 tháng 2 2021
Xét: \(\dfrac{1}{2}-\dfrac{1}{3}-\dfrac{1}{6}\)
\(=\dfrac{3-2-1}{6}\)
\(=0\)
\(\rightarrow C=0\)
BN
11 tháng 3 2022
1) âm năm phần 12
2) âm mười bảy phần 9
3) -1
Đây là đáp án còn làm bài từ làm nhé
L
7 tháng 9 2023
\(\dfrac{1}{6}+\dfrac{7}{12}-\dfrac{9}{20}+\dfrac{11}{30}-\dfrac{13}{42}\)
\(=\dfrac{1}{2.3}+\dfrac{7}{3.4}-\dfrac{9}{4.5}+\dfrac{11}{5.6}-\dfrac{13}{6.7}\)
\(=\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}+\dfrac{1}{4}-\left(\dfrac{1}{4}+\dfrac{1}{5}\right)+\dfrac{1}{5}+\dfrac{1}{6}-\left(\dfrac{1}{6}+\dfrac{1}{7}\right)\)
\(=\dfrac{1}{2}-\dfrac{1}{7}=\dfrac{5}{14}\)
3 tháng 8 2021
a) \(\dfrac{1}{2}< \dfrac{x}{9}< \dfrac{y}{18}< \dfrac{2}{3}\)
\(\Leftrightarrow\dfrac{9}{18}< \dfrac{2x}{18}< \dfrac{y}{18}< \dfrac{12}{18}\)
\(\Leftrightarrow\left\{{}\begin{matrix}2x=10\\y=11\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=5\\y=11\end{matrix}\right.\)
b) \(\dfrac{-1}{2}< \dfrac{x}{15}< \dfrac{y}{30}< \dfrac{-2}{5}\)
\(\Leftrightarrow\dfrac{-15}{30}< \dfrac{2x}{30}< \dfrac{y}{30}< \dfrac{-12}{30}\)
\(\Leftrightarrow\left\{{}\begin{matrix}2x=-14\\y=-13\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=-7\\y=-13\end{matrix}\right.\)
S
19 tháng 4 2023
a/\(\left(\dfrac{7}{9}\times\dfrac{9}{7}\right)\times\dfrac{25}{28}\)
\(=1\times\dfrac{25}{28}\)
\(=\dfrac{25}{28}\)
b/\(\dfrac{4}{7}\times\dfrac{17}{18}\times\dfrac{7}{4}\times\dfrac{18}{17}\)
\(=\left(\dfrac{4}{7}\times\dfrac{7}{4}\right)\times\left(\dfrac{17}{18}\times\dfrac{18}{17}\right)\)
\(=1\times1\)
\(=1\)
NT
Nguyễn Thị Thương Hoài
Giáo viên
VIP
14 tháng 4 2023
A = \(\dfrac{1}{20}\) + \(\dfrac{1}{30}\) + \(\dfrac{1}{42}\) + \(\dfrac{1}{56}\) + \(\dfrac{1}{72}\) + \(\dfrac{1}{90}\) + \(\dfrac{1}{110}\) + \(\dfrac{1}{132}\)
A = \(\dfrac{1}{4\times5}\) + \(\dfrac{1}{5\times6}\) + \(\dfrac{1}{6\times7}\)+ \(\dfrac{1}{7\times8}\)+\(\dfrac{1}{8\times9}\)+ \(\dfrac{1}{9\times10}\) + \(\dfrac{1}{10\times11}\)+\(\dfrac{1}{11\times12}\)
A = \(\dfrac{1}{4}\)-\(\dfrac{1}{5}\) +\(\dfrac{1}{5}\)-\(\dfrac{1}{6}\) +.....+\(\dfrac{1}{11}\) - \(\dfrac{1}{12}\)
A = \(\dfrac{1}{4}\) - \(\dfrac{1}{12}\)
A = \(\dfrac{1}{6}\)
DA
1
23 tháng 10 2023
ta nhận thấy
1/2=1-1/2
1/6=1/2-1/3
1/12=1/3-1/4
1/20=1/4-1/5
1/30=1/5-1/6
1/42=1/6-1/7
ta có:
1/2+1/6+1/12+1/20+1/30+1/42
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7
=1-1/7
=6/7
bn tự hiểu nha
23 tháng 5 2022
\(=\left(\dfrac{1}{21}+\dfrac{1}{210}+\dfrac{1}{2010}\right)\cdot\dfrac{10-6-3-1}{30}=0\)
C
23 tháng 5 2022
\(\left(\dfrac{1}{3}-\dfrac{1}{5}-\dfrac{1}{10}-\dfrac{1}{30}\right)\times\left(\dfrac{1}{21}+\dfrac{1}{210}+\dfrac{1}{2010}\right)\)
\(=\left(\dfrac{10}{30}-\dfrac{6}{30}-\dfrac{3}{30}-\dfrac{1}{30}\right)\times\left(\dfrac{1}{21}+\dfrac{1}{210}+\dfrac{1}{2010}\right)\)
\(=0\times\left(\dfrac{1}{21}+\dfrac{1}{210}+\dfrac{1}{2010}\right)\)
\(=0\)
A = \(\dfrac{1}{9}\) + \(\dfrac{1}{18}\) + \(\dfrac{1}{30}\) + ......+ \(\dfrac{1}{135}\)
A = \(\dfrac{1}{3}\) ( \(\dfrac{1}{3}\) + \(\dfrac{1}{6}\) + \(\dfrac{1}{10}\) +........+ \(\dfrac{1}{45}\))
A = \(\dfrac{2}{3}\) ( \(\dfrac{1}{6}\) + \(\dfrac{1}{12}\) + \(\dfrac{1}{20}\) +.....+\(\dfrac{1}{90}\))
A = \(\dfrac{2}{3}\) ( \(\dfrac{1}{2\times3}\) + \(\dfrac{1}{3\times4}\) + \(\dfrac{1}{4\times5}\)+......+\(\dfrac{1}{9\times10}\))
A = \(\dfrac{2}{3}\)( \(\dfrac{1}{2}\) - \(\dfrac{1}{3}\)+ \(\dfrac{1}{3}\)- \(\dfrac{1}{4}\)+ \(\dfrac{1}{4}\)- \(\dfrac{1}{5}\)+........+ \(\dfrac{1}{9}\)- \(\dfrac{1}{10}\))
A = \(\dfrac{2}{3}\)( \(\dfrac{1}{2}\)- \(\dfrac{1}{10}\))
A = \(\dfrac{2}{3}\) x( \(\dfrac{5}{10}\) - \(\dfrac{1}{10}\))
A = \(\dfrac{2}{3}\)x \(\dfrac{4}{10}\)
A = \(\dfrac{4}{15}\)
ai giúp mình nhanh đi mà