1+1=2

1+1+1=3

1+1+1+1=4

1+1+1+1+1=5

k nhé

= 2

=3

=4

=5

hok tốt nha !!!

21 tích đúng mìh 

=21

k nha

mong moi nguoi ung ho

ai k mình mình k lại

   I don' know

16/27 10000000000000000000000000000000000000000% luon

\(\left(1-\frac{1}{2}\right).\left(1-\frac{1}{3}\right).\left(1-\frac{1}{4}\right).\left(1-\frac{1}{5}\right)\)

\(=\frac{2}{3}.\frac{3}{4}.\frac{4}{5}.\frac{5}{6}\)

\(=\frac{2}{6}\)

\(=\frac{1}{3}\)

\(\left(1-\frac{1}{2}\right).\left(1-\frac{1}{3}\right).\left(1-\frac{1}{4}\right).\left(1-\frac{1}{5}\right)\)

\(=\frac{1}{2}.\frac{2}{3}.\frac{3}{4}.\frac{4}{5}\)

\(=\frac{1}{5}\)

\(\left(1-\frac{1}{4}\right).\left(1-\frac{1}{9}\right).....\left(1-\frac{1}{36}\right)\)

\(=\frac{3}{4}.\frac{8}{9}....\frac{35}{36}\)

\(=\frac{1.3}{2.2}.\frac{2.4}{3.3}.\frac{3.5}{4.4}.\frac{4.6}{5.5}.\frac{5.7}{6.6}\)

\(=\frac{7}{2.6}=\frac{7}{12}\)

P/S: dấu "." là dấu nhân nhé

B=3/2x4/3x...........x2018/2017

=3x4x5x...........x2018/2x3x2x2x............x2017

=2x2018

=4036

A,C tương tự

Mình nghĩ bài 1 đề sai .

bài 1 và bài 2 sai đề

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

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

\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}\)

\(=1-\frac{1}{5}\)

\(=\frac{4}{5}\)

\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{9900}\)

\(=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{98.99}+\frac{1}{99.100}\)

\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+....+\frac{1}{98}-\frac{1}{99}+\frac{1}{99}-\frac{1}{100}+\frac{1}{100}\)

\(=1-\frac{1}{100}\)

\(=\frac{99}{100}\)

Từng ý một nhanh hơn nhá

(1):= 1/2 : 2/3 : 3/4 = 3/4 : 3/4 =1

(2):= 3/2 * 4/3 * 5/4 = 2 * 5/4 = 5/2

mk k chép lại đề bài đâu, làm lun đó

A=1/2*2/3*3/4*4/5*...*99/100

sau đó n=dễ ợt mà