Tính nhanh:
1/24+1/96+1/240+...+1/2880
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\(\frac{1}{3}+\frac{1}{6}+\frac{1}{12}+\frac{1}{24}+\frac{1}{48}+\frac{1}{96}\)
\(=\frac{1}{2}+\frac{1}{8}+\frac{1}{32}\)
\(=\frac{5}{8}+\frac{1}{32}\)
\(=\frac{21}{32}\)
\(=2\left(\frac{1}{3}+\frac{1}{6}+...+\frac{1}{192}\right)\)
\(=2\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{6}+...+\frac{1}{96}-\frac{1}{192}\right)\)
\(=2\left(1-\frac{1}{192}\right)\)
\(=2\times\frac{191}{192}\)
\(=\frac{191}{96}\)
Giải
\(\frac{1}{6}+\frac{1}{12}+\frac{1}{24}+\frac{1}{48}+\)\(\frac{1}{96}\)
\(=\frac{1}{3}-\frac{1}{6}+\frac{1}{6}-\frac{1}{12}\)\(+\frac{1}{12}-\frac{1}{24}+\frac{1}{24}-\frac{1}{48}\)\(+\frac{1}{48}-\frac{1}{96}\)
\(=\frac{1}{3}-\frac{1}{96}\)
\(=\frac{31}{96}\)
1/6 + 1/12 + 1/24 + 1/48 + 1/96
= 1/3 - 1/6 + 1/6 - 1/12 + 1/12 - 1/24 + 1/24 - 1/48 + 1/48 - 1/96
= 1/3 - 1/96
= 31/96
a)
`6/9=2/3`
`6/24=1/4`
`48/96=1/2`
`42/98=3/7`
b)
`24/36=2/3`
`18/30=3/5`
`15/120=1/8`
`80/240=1/3`
a)\(\dfrac{6}{9}=\dfrac{6:3}{9:3}=\dfrac{2}{3}\)
\(\dfrac{6}{24}=\dfrac{6:6}{24:6}=\dfrac{1}{4}\)
\(\dfrac{48}{96}=\dfrac{48:48}{96:48}=\dfrac{1}{2}\)
\(\dfrac{42}{98}=\dfrac{42:14}{98:14}=\dfrac{3}{7}\)
b)\(\dfrac{24}{36}=\dfrac{24:12}{36:12}=\dfrac{2}{3}\)
\(\dfrac{18}{30}=\dfrac{18:6}{30:6}=\dfrac{3}{5}\)
\(\dfrac{15}{120}=\dfrac{15:15}{120:15}=\dfrac{1}{8}\)
\(\dfrac{80}{240}=\dfrac{80:80}{240:80}=\dfrac{1}{3}\)
\(\frac{1}{3}+\frac{1}{6}+\frac{1}{12}+\frac{1}{24}+\frac{1}{48}+\frac{1}{96}\)
\(=\left(\frac{1}{3}+\frac{1}{6}\right)+\left(\frac{1}{12}+\frac{1}{24}\right)+\left(\frac{1}{48}+\frac{1}{96}\right)\)
\(=\frac{1}{2}+\frac{1}{8}+\frac{1}{32}\)
\(=\frac{21}{32}\)
Biểu thức toán học kia có giá trị là
124+196+1240+...+12880=116
1/16