A=-(1/1.3+1/3.5+1/5.7+...+1/97.99)
A=-1/2.(2/1.3+2/3.5+2/5.7+...+2/97.99)
A=-1/2.(1-1/3+1/3-1/5+...+1/97-1/99)
A=-1/2.(1-1/99)=-1/2.98/99
A=(tự bấm máy tính nha)
lam j co tru o dang trc 1/99*97 sai tram trong
\(\frac{1}{99.97}-\frac{1}{97.95}-...-\frac{1}{5.3}-\frac{1}{3.1}\)
\(=\frac{1}{99.97}-\left(\frac{1}{1.3}+\frac{1}{3.5}+...+\frac{1}{95.97}\right)\)
\(=\frac{1}{99.97}-\frac{1}{2}.\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{95}-\frac{1}{97}\right)\)
\(=\frac{1}{9603}-\frac{1}{2}.\left(1-\frac{1}{97}\right)\)
\(=\frac{1}{9603}-\frac{1}{2}.\frac{96}{97}\)
\(=\frac{1}{9603}-\frac{48}{97}\)
\(=-\frac{4751}{9603}\)
