CMR:1- 1/2 + 1/3 - 1/4 + ... + 1/1989 - 1/1990 = 1/996 + 1/997 + ...1/1990
CMR: 1-1/2+1/3-1/4+...+1/1990=1/996+1/997+...+1/1990
CMR: 1-1/2+1/3-1/4+.....-1/1990=1/996+1/997+.....+1/1990
1,CMR:1-1/2-1/3-1/4-...-1/1990=1/996 1/997 ... 1/1990
CMR: (1-1/2+1/3-1/4+1/5-...-1/1990)=(1/996+1/997+...+1/1990)
1,CMR:\(1-\dfrac{1}{2}-\dfrac{1}{3}-\dfrac{1}{4}-...-\dfrac{1}{1990}=\dfrac{1}{996}+\dfrac{1}{997}+\dfrac{1}{1990}\)
1,CMR:\(1-\frac{1}{2}-\frac{1}{3}-\frac{1}{4}-...-\frac{1}{1990}=\frac{1}{996}+\frac{1}{997}+\frac{1}{1990}\)
cmr 1-\(\frac{1}{2}+\frac{1}{3}-\frac{1}{4}+.......-\frac{1}{1990}=\frac{1}{996}+\frac{1}{997}+\frac{1}{998}+.......+\frac{1}{1990}\)
xét vế trái
=(1+1/3+1/5+...+1/1989)-(1/2+1/4+...+1/1990)
=(1+1/2+1/3+1/4+...+1/1990)-2.(1/2+1/4+...+1/1990)
=(1+1/2+1/3+1/4+...+1/1990)-!1+1/2+1/3+1/4+...+1/995)
=1/996+1/997+.../1+1990
vậy 1-1/2+1/3-1/4+...-1/1990=1/996+1/997+...+1/1990
cmr 1-$\frac{1}{2}+\frac{1}{3}-\frac{1}{4}+.......-\frac{1}{1990}=\frac{1}{996}+\frac{1}{997}+\frac{1}{998}+.......+\frac{1}{1990}$
dòng dấu = thứ 3 sửa ! thành ( nha
chứng tỏ rằng 1 - 1/2 + 1/3 - 1/4 + .... - 1/1990 = 1/996 + 1/997 + 1/998 + ... + 1/1990
Chứng minh:
1-1/2+1/3+1/4+...+1/1990=1/996+1/997+1/1990
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