1/2.4.6 +1/4.6.8+1/6.8.10+1/8.10.12+1/10.12 .14+..1/96.98.100
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NL
2
8 tháng 5 2018
\(A=\frac{2}{2.4.6}+\frac{2}{4.6.8}+\frac{2}{6.8.10}+\frac{2}{8.10.12}\)
\(A=\frac{2}{48}+\frac{2}{192}+\frac{2}{480}+\frac{2}{960}\)
\(A=\frac{1}{24}+\frac{1}{96}+\frac{1}{240}+\frac{1}{480}\)
\(A=\frac{20}{480}+\frac{5}{480}+\frac{2}{480}+\frac{1}{480}\)
\(A=\frac{7}{120}\)
NT
Nguyễn Thị Thương Hoài
Giáo viên
VIP
14 tháng 3
A = \(\dfrac{2}{2.4.6}\) + \(\dfrac{2}{4.6.8}\) + \(\dfrac{2}{6.8.10}\) + \(\dfrac{2}{8.10.12}\)
A = \(\dfrac{2}{2}\).(\(\dfrac{2}{2.4.6}\) + \(\dfrac{2}{4.6.8}\) + \(\dfrac{2}{6.8.10}\) + \(\dfrac{2}{8.10.12}\))
A = \(\dfrac{1}{2}\).(\(\dfrac{2.2}{2.4.6}\) + \(\dfrac{2.2}{4.6.8}\) + \(\dfrac{2.2}{6.8.10}+\dfrac{2.2}{8.10.12}\))
A = \(\dfrac{1}{2}\).( \(\dfrac{4}{2.4.6}+\dfrac{4}{4.6.8}+\dfrac{4}{6.8.10}+\dfrac{4}{8.10.12}\))
A = \(\dfrac{1}{2}\).(\(\dfrac{1}{2.4}\) - \(\dfrac{1}{4.6}\) +\(\dfrac{1}{4.6}\) - \(\dfrac{1}{6.8}\) + \(\dfrac{1}{6.8}\) - \(\dfrac{1}{8.10}\) + \(\dfrac{1}{8.10}\) - \(\dfrac{1}{10.12}\))
A = \(\dfrac{1}{2}\).(\(\dfrac{1}{2.4}\) - \(\dfrac{1}{10.12}\))
A = \(\dfrac{1}{2}\).(\(\dfrac{1}{8}-\dfrac{1}{120}\))
A = \(\dfrac{1}{2}\).\(\dfrac{7}{60}\)
A = \(\dfrac{7}{120}\)
DD
A = \(\frac{2.4.6+4.6.8+6.8.10+8.10.12+...+198.200.202}{1.3.5+3.5.7+5.7.9+7.9.11+...+97.99.101}\) =?
0
TG
0
TG
0
MA
0
HN
3
23 tháng 3 2017
Ta có A = \(\frac{1.2.3-2.3.4+3.4.5-4.5.6+5.6.7-6.7.8}{2.4.6-4.6.8+6.8.10-8.10.12+10.12.14-12.14.16}\)
A = \(\frac{1.2.3-2.3.4+3.4.5-4.5.6+5.6.7-6.7.8}{\left(1.2.3\right).2-\left(2.3.4\right).2+\left(3.4.5\right).2-\left(4.5.6\right).2+\left(5.6.7\right).2-\left(6.7.8\right).2}\)
A = \(\frac{1.\left(1.2.3-2.3.4+3.4.5-4.5.6+5.6.7-6.7.8\right)}{2.\left(1.2.3-2.3.4+3.4.5-4.5.6+5.6.7-6.7.8\right)}\)
A = \(\frac{1}{2}\)