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\(A=\frac{3}{54}+\frac{5}{126}+\frac{7}{294}+\frac{8}{609}\)
\(\Rightarrow A=\frac{3}{9.6}+\frac{5}{2.7.9}+\frac{7}{7.7.6}+\frac{8}{3.7.29}\)
\(\Rightarrow A=\frac{1}{18}+\frac{5}{7.18}+\frac{1}{6.7}+\frac{8}{3.7.29}\)
\(\Rightarrow A=\frac{7+5}{7.18}+\frac{1}{6.7}+\frac{8}{3.7.29}\)
\(\Rightarrow A=\frac{2}{7.3}+\frac{1}{6.7}+\frac{8}{3.7.29}\)
\(\Rightarrow A=\frac{1}{3.7}\left(\frac{2}{1}+\frac{1}{2}+\frac{8}{29}\right)\)
\(\Rightarrow A=\frac{1}{21}\left(\frac{116+29+16}{58}\right)\)
\(\Rightarrow A=\frac{1}{21}.\frac{161}{58}\)
\(\Rightarrow A=\frac{161}{1218}=\frac{23}{174}\)
Vậy \(A=\frac{23}{174}\)
kết quả đúng rồi cậu ơi , nhg cách làm sai , zới lại câu giải muộn quá nên tớ làm được rồi , dù sao cũng THANKS 
A=3/54+5/126+7/294+8/609
=1/18+5/126+1/42+8/609
=2/21+15/406
=23/174
tick cho mik nha
a = 3/54 + 5/126 + 7/294 + 8/609 + 13/1218
=> a = 3/6.9 + 5/9.14 + 7/14.21 + 8/21.29 + 13/29.42
=> a = 1/6 - 1/9 + 1/9 - 1/14 + 1/14 - 1/21 + 1/21 - 1/29 + 1/29 - 1/42
=> a = 1/6 - 1/42
=> a = 7/42 - 1/42
=> a = 6/42 = 1/7
1+2-3-4+5+6-7-8+...+111-112+113+114+115
=1+(2-3-4+5)+(6-7-8+9)+....................................+(110-111-112+113)+114+115
=230
\(\frac{3}{54}+\frac{5}{126}+\frac{7}{294}+\frac{8}{609}\)
\(=\frac{3}{6.9}+\frac{5}{9.14}+\frac{7}{14.21}+\frac{8}{21.29}\)
\(=\frac{1}{6}-\frac{1}{9}+\frac{1}{9}-\frac{1}{14}+\frac{1}{14}-\frac{1}{21}+\frac{1}{21}-\frac{1}{29}\)
\(=\frac{1}{6}-\frac{1}{29}=\frac{23}{174}\)
A=\(\frac{3}{9.6}+\frac{5}{2.7.9}+\frac{7}{6.7.7}+\frac{8}{3.7.29}\) = \(\frac{1}{18}+\frac{5}{7.18}+\frac{1}{6.7}+\frac{8}{3.7.29}\)
= \(\frac{7+5}{7.18}+\frac{1}{6.7}+\frac{8}{3.7.29}\)=\(\frac{2}{7.3}+\frac{1}{6.7}+\frac{8}{3.7.29}\)= \(\frac{1}{3.7}.\)(\(\frac{2}{1}+\frac{1}{2}+\frac{8}{29}\))=
=\(\frac{1}{21}.\)(\(\frac{116+29+16}{58}\))=\(\frac{1}{21}.\frac{161}{58}=\frac{161}{1218}\)