Question

Tính tổng dãy số sau :  \(A=\frac{5}{2}+\frac{5}{6}+\frac{5}{12}+\frac{5}{20}+....+\frac{5}{9506}+\frac{5}{9702}+\frac{5}{9900}\)

Answer 1

A= 5.(1/2 + 1/6+1/12+1/20+...+1/9506+1/9702+1/9900)

 = 5. (1/1.2 + 1/2.3+1/3.4+1/4.5+...1/97.98+1/98.99+1/99.100)

= 5 .(1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+...+1/97-1/98+1/98-1/99+1/99-1/100)

= 5.(1-1/100)=5. 99/100=99/20

Answer 2

25

5144 nhe