Question

cho E=1/1.101+1/2.102+1/3.103+...+1/10.110

và F=1/1.11+1/2.12+1/3.13+...+1/100.110

tính E:F

 

Answer 1

\(\dfrac{1}{10}nhébạn\)

Answer 2

E = 1/1.101+1/2.102+...+1/10.110

E = 1/100[100/1.101+100/2.102+...+100/10.110]

E = 1/100[1/1-1/101+1/2-1/102+...+1/10-1/110]

E = 1/100[[1/1+1/2+1/3...+1/10]-[1/101+1/102+...+1/110] - xg cái E

F = 1/1.11+1/2.12+...+1/100.110

F = 1/10[10/1.11+10/2.12+...+10/100.110]

F = 1/10[1/1-1/11+1/2-1/12+...+1/100-1/110]

F = 1/10[[1/1+1/2+...+1/100]-[1/11+1/12...+1/110]]

F = 1/10[[1/1+1/2+...+1/10]-[1/101+1/102+...+1/110]

⇒EF=1100[[11+12+...+110]−[1101+1102+...+1110]]110[[11+12+...+110]−[1101+1102+...+1110]]=110