\(A=3\cdot\left(\frac{1}{5}+\frac{1}{25}+\frac{1}{125}+\frac{1}{625}\right)\)
\(A=3\cdot\left(\frac{125}{625}+\frac{25}{625}+\frac{5}{625}+\frac{1}{625}\right)\)
\(A=\frac{3\cdot156}{625}\)
\(A=\frac{468}{625}\)
~Tham khảo nha~
\(A=3\times\left(\frac{1}{5}+\frac{1}{25}+\frac{1}{125}+\frac{1}{625}\right)\)
\(A=3\times\left(\frac{125}{625}+\frac{25}{625}+\frac{5}{625}+\frac{1}{625}\right)\)
\(A=\frac{3\times156}{625}\)
\(A=\frac{468}{625}=0,7488\)
\(A=\frac{3}{5}+\frac{3}{25}+\frac{3}{125}+\frac{3}{625}\)
\(A=3.\left(\frac{1}{5}+\frac{1}{25}+\frac{1}{125}+\frac{1}{625}\right)\)
Đặt \(B=\frac{1}{5}+\frac{1}{25}+\frac{1}{125}+\frac{1}{625}\)
\(\Rightarrow5B=1+\frac{1}{5}+\frac{1}{25}+\frac{1}{125}\)
\(\Leftrightarrow5B-B=1-\frac{1}{625}\)
\(4B=1-\frac{1}{625}=\frac{624}{625}\)
\(\Rightarrow B=\frac{624}{625}:4=\frac{156}{625}\)
Thay B vào A
có: \(A=3\cdot\frac{156}{625}=\frac{468}{625}\)
\(A=\frac{3}{5}+\frac{3}{25}+\frac{3}{125}+\frac{3}{625}\)
\(5A=3+\frac{3}{5}+\frac{3}{25}+\frac{3}{125}\)
\(5A-A=\left(3+\frac{3}{5}+\frac{3}{25}+\frac{3}{125}\right)-\left(\frac{3}{5}+\frac{3}{25}+\frac{3}{125}+\frac{3}{625}\right)\)
\(4A=3-\frac{3}{625}\)
\(A=\frac{468}{625}\)