Question

1+1/5+1/25+.........+1/15625

mọi người giúp em làm  câu này với ạ

em cảm ơn

 

Answer 1

Sửa đề thành : S=1+1/5+1/25+.........+1/15625 

5xS=1+1/5+1/25+....+1/3125

5xS-S=(1+1/5+1/25+...+1/3125)-(1/5+1/25+1/125+....+1/15625)

4xS=1-1/15625=15624/15625

1xS=15624/15625:4=15624/15625x1/4=15624/62500=3906/15625

Answer 2

\(#040510\)

\(S=1+\dfrac{1}{5}+\dfrac{1}{25}+...+\dfrac{1}{15625}\)

\(5S=5+1+\dfrac{1}{5}+...+\dfrac{1}{3125}\)

\(5S-S=5-\dfrac{1}{15625}\)

\(S=\dfrac{5.15625-1}{4.15625}\)

\(S=\dfrac{78124}{4.15625}=\dfrac{19531}{15625}\)