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\(a,2,5\cdot x=\frac{11}{15}\)
\(\Rightarrow x=\frac{11}{15}:2,5\)
\(\Rightarrow x=\frac{11}{15}:\frac{25}{10}\)
\(\Rightarrow x=\frac{11}{15}\cdot\frac{10}{25}\)
\(\Rightarrow x=\frac{11}{3}\cdot\frac{2}{25}=\frac{22}{75}\)
\(b,x-15\%\cdot x=\frac{1}{3}\)
\(\Rightarrow x-\frac{15}{100}\cdot x=\frac{1}{3}\)
\(\Rightarrow x-\frac{3}{20}\cdot x=\frac{1}{3}\)
\(\Rightarrow\frac{20x}{20}-\frac{3x}{20}=\frac{1}{3}\)
\(\Rightarrow\frac{17x}{20}=\frac{1}{3}\)
\(\Rightarrow17x\cdot3=20\)
\(\Rightarrow17x=\frac{20}{3}\)
\(\Rightarrow x=\frac{20}{3}:17=\frac{20}{3}\cdot\frac{1}{17}=\frac{20}{51}\)
Câu c mk làm sau :v
c,\(\left[\frac{3x}{7}+1\right]:\left[-4\frac{1}{7}\right]=\frac{-3}{28}\)
\(\Rightarrow\left[\frac{3x}{7}+1\right]:\left[-\frac{29}{7}\right]=\frac{-3}{28}\)
\(\Rightarrow\frac{3x}{7}+1=-\frac{3}{28}\cdot-\frac{29}{7}=\frac{87}{196}\)
\(\Rightarrow\frac{3x}{7}=\frac{87}{196}-1\)
Tìm nốt :v
(1-1/3).(1-1/5).(1-1/7).(1-1/9).(1-1/11).(1-1/13).(1-1/2).(1-1/4).(1-1/6).(1-1/8).(1-1/10)
=2/3.4/5.6/7.8/9.10/11.12/13.1/2.3/4.5/6.7/8.9/10
=8/15.48/63.120/143.3/8.35/48.9/10
=384/945.360/1144.315/480
=138240/1081080.315/480
=43545600/518918400=84/1001
\(\left(1-\frac{1}{2}\right)\left(1-\frac{1}{3}\right)\left(1-\frac{1}{4}\right)....\left(1-\frac{1}{2009}\right)\)
=\(\frac{1}{2}.\frac{2}{3}.\frac{3}{4}...\frac{2008}{2009}\)
=\(\frac{1}{2009}\)
a,\(\frac{5}{3}.\frac{3}{7}+\frac{5}{3}.\frac{5}{7}-\frac{5}{3}\)
=\(\frac{5}{3}.\left(\frac{3}{7}+\frac{5}{7}\right)-\frac{5}{3}\)
= \(\frac{5}{21}\)
\(\frac{11}{36}-\left(-\frac{7}{24}\right)\)
\(=\frac{11}{36}+\frac{7}{24}\)
\(=\frac{22}{72}+\frac{21}{72}\)
\(=\frac{43}{72}\)
= 43/72 nha