Question

Tính :

1/2+1/6+1/12+1/20+1/30+...+1/90

Answer 1

1/2+1/6+1/12+1/20+1/30+...+1/90=

1/1*2+1/2*3+1/3*4+...+1/9*10=1/1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+...+1/9-1/10=

1/1-1/10=9/10 ban a

Answer 2

1/2+1/6+1/12+1/20+1/30+...+1/90

=1/1.2+1/2.3+1/3.4+1/4.5+1/5.6+...+1/9.10

=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+...+1/9-1/10

=1-1/10

=9/10

Answer 3

\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+...+\frac{1}{90}\)

\(=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+...+\frac{1}{9.10}\)

\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+...+\frac{1}{9}-\frac{1}{10}\)

\(=1-\frac{1}{10}\)

\(=\frac{9}{10}\)

k nha

Answer 4

1/2+1/6+1/12+1/20+1/30+...+1/90

=1/1.2+1/2.3+1/3.4+1/4.5+1/5.6+...+1/9.10

=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+...+1/9-1/10

=1-1/10

=9/10

Answer 5

9/10 nhé