Question

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

tính nhanh nhé!

thứ 7 phải nộp rồi!

 

Answer 1

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

1-1/2+1/2-1/3+...+1/9-1/10

1-1/10

9/10

đúng 100% đấy

Answer 2

dai lam

Answer 3

=1/1.2+1/2.3+...+1/9.10

=1-1/2+1/2-1/3+...+1/9-1/10

=1-1/10

=9/10

Ti ck nha bạn

Answer 4

Bạn tham khảo bài này nha!:

A=1/2.3+1/3.4+1/4.5+1/5.6+1/6.7+1/7.8+1/8.9+1/9.10+1/10.11
A=1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10+1/10-1/11
A=1/2-(1/3-1/3)-(1/4-1/4)-(1/5-1/5)-(1/6-1/6)-(1/7-1/7)-(1/8-1/8)-(1/9-1/9)-(1/10-1/10)-1/11
A=1/2-1/11
A=11/22-2/22
A=9/22

Answer 5

ta có:

\(\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{9.10}\)

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

\(=1-\frac{1}{10}=\frac{9}{10}\)

học tốt nh!!!

Answer 6

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

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

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

= \(\frac{1}{1}-\frac{1}{10}\)

= \(1-\frac{1}{10}\)

= \(\frac{9}{10}\)