5.
S = 1/2 + 1/6 +1/12+...+1/45.46
S = 1/1.2 +1/2.3 +...+ 1/45.46
S = 1 - 1/2 + 1/2 - 1/3 +...+1/45-1/46
S = 1 - 1/46
S = 45/46
P = 2/2.4 + 2/4.6 + ....+ 2/2008.2010
P = 1 - 1/4 + 1/4 - 1/6 + ..... + 1/2008-1/2010
P = 1 - 1/2010
P = 2009/2010
HỌC TỐT :D