Tính nhanh 2/35 + 4/77 + 2/143 + 4/221 + 2/323 + 4/437 + 2/575
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H
1
13 tháng 8 2016
\(\frac{2}{35}+\frac{4}{77}+\frac{2}{143}+\frac{4}{221}+\frac{2}{323}+\frac{4}{437}+\frac{2}{575}\)
\(=\frac{2}{5.7}+\frac{4}{7.11}+\frac{2}{11.13}+\frac{4}{13.17}+\frac{2}{17.19}+\frac{4}{19.23}+\frac{2}{23.25}\)
\(=\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{17}+\frac{1}{17}-\frac{1}{19}+\frac{1}{19}-\frac{1}{23}+\frac{1}{23}-\frac{1}{25}\)
\(=\frac{1}{5}-\frac{1}{25}\)
\(=\frac{5}{25}-\frac{1}{25}=\frac{4}{25}\)
13 tháng 8 2015
2/35 + 4/77 + 2/143 + 4/221 + 2/323 + 4/437 + 2/575
= 2/5.7 + 4/7.11 + 2/11.13 + 4/13.17 + 2/17.19 + 4/19.23 + 2/23.25
= 1/5 - 1/7 + 1/7 - 1/11 + 1/11 - 1/13 + 1/13 - 1/17 + 1/17 - 1/19 + 1/19 - 1/23 + 1/23 - 1/15
= 1/5 - 1/25
= 4/25
li ke cho mk nha
MT
14 tháng 7 2015
\(J=\frac{2}{35}+\frac{4}{77}+\frac{2}{143}+\frac{4}{221}+\frac{2}{323}+\frac{4}{437}+\frac{2}{575}\)
\(=\frac{2}{5\times7}+\frac{4}{7\times11}+\frac{2}{11\times13}+\frac{4}{13\times17}+\frac{2}{17\times19}+\frac{4}{19\times23}+\frac{2}{23\times25}\)
\(=\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{17}+\frac{1}{17}-\frac{1}{19}+\frac{1}{19}-\frac{1}{23}+\frac{1}{23}-\frac{1}{25}\)
\(=\frac{1}{5}-\frac{1}{25}=\frac{5}{25}-\frac{1}{25}=\frac{4}{25}\)
NT
Nguyễn Thị Thương Hoài
Giáo viên
VIP
4 tháng 4 2023
A = \(\dfrac{2}{35}\) + \(\dfrac{4}{77}\) + \(\dfrac{2}{143}\) + \(\dfrac{4}{221}\) + \(\dfrac{2}{323}\) + \(\dfrac{4}{437}\) + \(\dfrac{2}{575}\)
A = \(\dfrac{2}{5\times7}\)+\(\dfrac{4}{7\times11}\)+\(\dfrac{2}{11\times13}\)+\(\dfrac{4}{13\times17}\)+\(\dfrac{2}{17\times19}\)+\(\dfrac{4}{19\times23}\)+\(\dfrac{2}{23\times25}\)
A = \(\dfrac{1}{5}\)-\(\dfrac{1}{7}\)+ \(\dfrac{1}{7}\) - \(\dfrac{1}{11}\)+\(\dfrac{1}{11}\)-\(\dfrac{1}{13}\)+\(\dfrac{1}{13}\)-\(\dfrac{1}{17}\)+\(\dfrac{1}{17}\)-\(\dfrac{1}{19}\)+\(\dfrac{1}{19}\)-\(\dfrac{1}{23}\)+\(\dfrac{1}{23}\)-\(\dfrac{1}{25}\)
A = \(\dfrac{1}{5}\) - \(\dfrac{1}{25}\)
A = \(\dfrac{4}{25}\)
H
2
NT
18 tháng 7 2018
2/35 + 4/77 + 2/143 + 4/221 + 2/323 + 4/437 + 2/575
= 2/5.7 + 4/7.11 + 2/11.13 + 4/13.17 + 2/17.19 + 4/19.23 + 2/23.25
= 1/5 - 1/7 + 1/7 - 1/11 + 1/11 - 1/13 + 1/13 - 1/17 + 1/17 - 1/19 + 1/19 - 1/23 + 1/23 - 1/15
= 1/5 - 1/25
= 4/25
18 tháng 7 2018
\(\frac{2}{35}\)+ \(\frac{4}{77}\)+ \(\frac{2}{143}\)+ \(\frac{4}{221}\)+ \(\frac{2}{323}\)+ \(\frac{4}{437}\)+ \(\frac{2}{575}\).
= \(\frac{2}{5.7}\)+ \(\frac{4}{7.11}\)+ \(\frac{2}{11.13}\)+ \(\frac{4}{13.17}\)+ \(\frac{4}{17.21}\)+ \(\frac{2}{21.23}\).
= \(\frac{1}{5}\)- \(\frac{1}{7}\)+ \(\frac{1}{7}\)- \(\frac{1}{11}\)+ \(\frac{1}{11}\)- \(\frac{1}{13}\)+ \(\frac{1}{13}\)- \(\frac{1}{17}\)+ \(\frac{1}{17}\)- \(\frac{1}{21}\)+ \(\frac{1}{21}\)- \(\frac{1}{23}\).
= \(\frac{1}{5}\)- \(\frac{1}{23}\).
= \(\frac{23}{115}\)- \(\frac{5}{115}\).
= \(\frac{18}{115}\).
NT
2
21 tháng 8 2018
2/35+4/77+2/143+4/221+2/333+4/437+2/575
=4/70+4/77+4/286+4/221+4/666+4/437+4/575
=4/35-4/575
=432/4025
21 tháng 8 2018
= 2/5 nhân 7+4/7 nhân 11+2/11 nhân 13+4/13 nhân 17+2/17 nhân 19+4/19 nhân 23+2/23 nhân 25
=1/5-1/25=4/25
KT
3 tháng 8 2018
\(A=\frac{2}{35}+\frac{4}{77}+\frac{2}{143}+\frac{4}{221}+\frac{2}{223}+\frac{4}{437}+\frac{2}{575}\)
\(=\frac{2}{5.7}+\frac{2}{7.11}+\frac{2}{11.13}+\frac{4}{13.17}+\frac{2}{17.19}+\frac{4}{19.23}+\frac{2}{23.25}\)
\(=\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{17}+\frac{1}{17}-\frac{1}{19}+\frac{1}{19}-\frac{1}{23}+\frac{1}{23}-\frac{1}{25}\)
\(=\frac{1}{5}-\frac{1}{25}\)
\(=\frac{4}{25}\)
5 tháng 8 2018
\(A=\frac{2}{35}+\frac{4}{77}+\frac{2}{143}+\frac{4}{221}+\frac{2}{323}+\frac{4}{437}+\frac{2}{575}\)
\(A=\frac{2}{5.7}+\frac{4}{7.11}+\frac{2}{11.13}+\frac{4}{13.17}+\frac{2}{17.19}+\frac{4}{19.23}+\frac{2}{23.25}\)
\(A=\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{17}+\frac{1}{17}-\frac{1}{19}+\frac{1}{19}-\frac{1}{23}+\frac{1}{23}-\frac{1}{25}\)
\(A=\frac{1}{5}-\frac{1}{25}=\frac{4}{25}\)
5 tháng 8 2018
\(A=\frac{2}{35}+\frac{4}{77}+\frac{2}{143}+\frac{4}{221}+\frac{2}{323}+\frac{4}{437}+\frac{2}{575}\)
\(A=\frac{2}{5.7}+\frac{4}{7.11}+\frac{2}{11.13}+\frac{4}{13.17}+\frac{2}{17.19}+\frac{4}{19.23}+\frac{2}{23.25}\)
\(A=1.\left(\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{13}+...+\frac{1}{19}-\frac{1}{23}+\frac{1}{23}-\frac{1}{25}\right)\)
A = 1/5 - 1/25
A = 4/25
NT
1
24 tháng 7 2018
\(\frac{2}{35}+\frac{4}{77}+\frac{2}{143}+\frac{4}{221}+\frac{2}{323}+\frac{4}{437}+\frac{2}{575}\)
\(=\frac{2}{5.7}+\frac{4}{7.11}+\frac{2}{11.13}+\frac{4}{13.17}+\frac{2}{17.19}+\frac{4}{19.23}+\frac{2}{23.25}\)
\(=\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+...+\frac{1}{19}-\frac{1}{23}+\frac{1}{23}-\frac{1}{25}\)
\(=\frac{1}{5}-\frac{1}{25}\)
\(=\frac{5}{25}-\frac{1}{25}\)
\(=\frac{4}{25}\)
P/S: Dấu "." là dấu nhân bạn nhé
4/25
cho **** cái