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1 tháng 4 2020
a) 7/10+6/10\(=\frac{13}{10}\)
b) -5/9+2/9\(=\frac{-1}{3}\)
c)1/7+1 6/7\(=2\)
d) 3/13+10/3+1\(=\frac{71}{26}\)
e) 5/12-7/12\(=\frac{-1}{6}\)
f) 7/6+5/6-1/6\(=\frac{11}{6}\)
g) -3/20+7/20-9/20\(=\frac{-1}{4}\)
học tốt
9 tháng 8 2017
a) \(\dfrac{7}{-25}+\dfrac{8}{25}=\dfrac{-7}{25}+\dfrac{8}{25}=\dfrac{1}{25}\)
\(\dfrac{4}{5}+\dfrac{4}{-18}=\dfrac{4}{5+\left(-18\right)}=\dfrac{4}{-13}=\dfrac{-4}{13}\)
\(\dfrac{7}{21}+\dfrac{9}{-36}=\dfrac{1}{3}+\dfrac{1}{-4}=\dfrac{1}{3+\left(-4\right)}=\dfrac{1}{-1}=1\)
b) \(\dfrac{12}{20}-\dfrac{2}{5}=\dfrac{12}{20}+\left(\dfrac{-2}{5}\right)=\dfrac{3}{5}+\dfrac{-2}{5}=\dfrac{3+\left(-2\right)}{5}=\dfrac{1}{5}\)
\(\dfrac{2}{3}-\dfrac{-5}{6}=\dfrac{2}{3}+\dfrac{5}{6}=\dfrac{4}{6}+\dfrac{5}{6}=\dfrac{9}{6}=\dfrac{3}{2}\)
\(6-\dfrac{3}{20}=6+\dfrac{-3}{20}=\dfrac{60}{60}+\dfrac{-9}{60}=\dfrac{51}{60}\)
c) \(\dfrac{2}{21}.\dfrac{-7}{3}=\dfrac{2.\left(-1\right)}{7.3}=\dfrac{-2}{21}\)
\(\dfrac{27}{28}.\left(-21\right)=\dfrac{27.\left(-21\right)}{28}=\dfrac{-567}{28}\)
\(\dfrac{-15}{7}.\dfrac{-14}{25}=\dfrac{-3.\left(-2\right)}{1.5}=\dfrac{6}{5}\)
15 tháng 4 2019
\(\left(19\frac{5}{8}:\frac{7}{12}-13\frac{1}{4}:\frac{7}{12}\right).\frac{4}{5}\)
\(=\left(\frac{157}{8}:\frac{7}{12}-\frac{53}{4}:\frac{7}{12}\right).\frac{4}{5}\)
\(=\left[\left(\frac{157}{8}-\frac{53}{4}\right):\frac{7}{12}\right].\frac{4}{5}\)
\(=\left[\frac{51}{8}:\frac{7}{12}\right].\frac{4}{5}\)
\(=\frac{153}{14}.\frac{4}{5}\)
\(=\frac{306}{35}\)
15 tháng 4 2019
\(\left(\frac{-2}{5}+\frac{3}{7}\right)-\left(\frac{4}{9}+\frac{12}{20}-\frac{13}{35}\right)+\frac{7}{35}\)
\(=\frac{1}{35}-\frac{212}{315}+\frac{7}{35}\)
\(=\frac{1}{35}+\frac{-212}{315}+\frac{7}{35}\)
\(=\frac{9}{315}+\frac{-212}{315}+\frac{63}{315}\)
\(=\frac{-140}{315}=\frac{-4}{9}\)
RD
0
DD
Đoàn Đức Hà
Giáo viên
1 tháng 3 2021
\(A=\frac{1}{6}+\frac{1}{7}+\frac{1}{8}+...+\frac{1}{20}\)
\(=\left(\frac{1}{6}+\frac{1}{7}+\frac{1}{8}\right)+\left(\frac{1}{9}+\frac{1}{10}+\frac{1}{11}\right)+\frac{1}{12}+\left(\frac{1}{13}+...+\frac{1}{16}\right)+\left(\frac{1}{17}+...+\frac{1}{20}\right)\)
\(>\left(\frac{1}{9}+\frac{1}{9}+\frac{1}{9}\right)+\left(\frac{1}{12}+\frac{1}{12}+\frac{1}{12}\right)+\frac{1}{12}+\left(\frac{1}{16}+...+\frac{1}{16}\right)+\left(\frac{1}{24}+...+\frac{1}{24}\right)\)
\(=\frac{1}{3}+\frac{1}{4}+\frac{1}{12}+\frac{1}{4}+\frac{1}{6}=1+\frac{1}{12}\)
\(B=\frac{1}{5}+\frac{1}{6}+...+\frac{1}{18}+\frac{1}{19}\)
\(=\left(\frac{1}{5}+...+\frac{1}{9}\right)+\left(\frac{1}{10}+...+\frac{1}{14}\right)+\left(\frac{1}{15}+...+\frac{1}{19}\right)\)
\(< \left(\frac{1}{5}+...+\frac{1}{5}\right)+\left(\frac{1}{10}+...+\frac{1}{10}\right)+\left(\frac{1}{15}+...+\frac{1}{15}\right)\)
\(=\frac{5}{5}+\frac{5}{10}+\frac{5}{15}=1+\frac{5}{6}\)
6 tháng 7 2020
Trả lời
a, \(3x=-75\)
\(x=-25\)
b \(\frac{x}{7}=\frac{-6}{8}\)
\(8x=-42\)
\(x=\frac{-21}{4}\)
c, \(\frac{-5}{6}+x=\frac{7}{12}-\frac{1}{3}\)
\(\frac{-5}{6}+x=\frac{1}{4}\)
\(x=\frac{13}{12}\)
d, \(\frac{1}{2}.x-\frac{33}{55}=\frac{20}{50}\)
\(\frac{1}{2}.x=1\)
\(x=2\)
Học tốt
6 tháng 7 2020
a, 3X = -75
X = -75 :3
X = -25
b, X x 7 = - 6 x 8
X x 7 = -48
X = -48 :7
X = -48/7
B= \(\dfrac{7}{6}+\dfrac{7}{12}+\dfrac{7}{20}+\dfrac{7}{30}+...+\dfrac{7}{1980}\)
B= \(\dfrac{7}{2\times3}+\dfrac{7}{3\times4}+\dfrac{7}{4\times5}+\dfrac{7}{5\times6}+...+\dfrac{7}{44\times45}\)
B= \(7\times\left(\dfrac{1}{2\times3}+\dfrac{1}{3\times4}+...+\dfrac{1}{44\times45}\right)\)
B= 7\(\times\) \(\left(\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{44}-\dfrac{1}{45}\right)\)
B= 7\(\times\) \(\left(\dfrac{1}{2}-\dfrac{1}{45}\right)\)
B= 7\(\times\) \(\dfrac{43}{90}\)
B= \(\dfrac{301}{90}\)