Question

Tổng S = -1/2 - 1/3 - 1/4 - .........-1/20 +3/2 +4/3 +5/4 +.....+21/20

Answer 1

\(-\frac{1}{2}-\frac{1}{3}-\frac{1}{4}-...-\frac{1}{20}+\frac{3}{2}+\frac{4}{3}+\frac{5}{4}+...+\frac{21}{20}\)

Answer 2

S=-1/2-1/3-1/4-...-1/20+3/2+4/3+5/4+...+21/20

=>S=(3/2-1/2)+(4/3-1/3)+(5/4-1/4)+...+(21/20-1/20)

=>S=1+1+1...+1

Ta thấy S có 20 số hạng

=>S=20