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Thời gian đi là 10h30'-6h30'=4h
Vận tốc là 40/4=10km/h
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1/2 + 1/6 + 1/12 + 1/20 +1/30
= 30/60 + 10/60 + 5/60 + 3/60 + 2/60
= (30+10+5+3+2)/60
= 50/60 = 5/6
\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}\)
\(=1-\frac{1}{2}+\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{6}\)
\(=1-\frac{1}{6}\)
\(=\frac{5}{6}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(A=\frac{1}{\frac{3.4}{2}}+\frac{1}{\frac{4.5}{2}}+...+\frac{1}{\frac{19.20}{2}}\)
=> \(A=\frac{2}{3.4}+\frac{2}{4.5}+...+\frac{2}{19.20}\)
=> \(\frac{A}{2}=\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{19.20}\)
=> \(\frac{A}{2}=\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{19}-\frac{1}{20}\)
=> \(\frac{A}{2}=\frac{1}{3}-\frac{1}{20}\)
=> \(\frac{A}{2}=\frac{20-3}{20.3}\)
=> \(\frac{A}{2}=\frac{17}{60}\)
=> \(A=\frac{17}{30}\)
VẬY \(A=\frac{17}{30}\)
Ta có :\(\frac{1}{1+2+3}+\frac{1}{1+2+3+4}+...+\frac{1}{1+2+3+...+19}\)
\(=\frac{1}{3\times4}\times2+\frac{1}{4\times5}\times2+...+\frac{1}{19\times20}\times2\)
\(=2\times\left(\frac{1}{3\times4}+\frac{1}{4\times5}+...+\frac{1}{19\times20}\right)=2\times\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{19}-\frac{1}{20}\right)\)
\(=2\times\left(\frac{1}{3}-\frac{1}{20}\right)=2\times\frac{17}{60}=\frac{17}{30}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(A=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{8}+...+\frac{1}{100}-\frac{1}{200}+\frac{1}{200}-\frac{1}{400}\)
\(A=1-\frac{1}{400}\)
\(A=\frac{399}{400}\)
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1/2 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56 + 1/72 + 1/90
=1/(1.2)+1/(2.3)+1/(3.4)+1/(4.5)
+1/(5.6)+1/(6.7)+1/(7.8)
+1/(8.9)+1/(9.10)
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5.+1/5-1/6...
+1/9-1/10
=1-1/10
=9/10
\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+...+\frac{1}{9.10}\)
\(=\frac{1}{1x2}+\frac{1}{2x3}+\frac{1}{3x4}+...+\frac{1}{9x10}\)
\(=\frac{2-1}{1x2}+\frac{3-2}{2x3}+\frac{4-3}{3x4}+...+\frac{10-9}{9x10}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}\)
\(=1-\frac{1}{10}\)
\(=\frac{10}{10}-\frac{1}{10}\)
\(=\frac{9}{10}\)
Tham khảo nha !!!
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7 và \(\frac{7}{100}\)dm2 = 0,0707 m2
Ai thấy đúng thì tk mình nha.
Y = 12 nhes
Ht
trình bày đâu bn ey