\(1\frac{1}{2}\times1\frac{1}{3}\times1\frac{1}{4}\)

=\(\frac{3}{2}\times\frac{4}{3}\times\frac{5}{4}\)

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

=\(\frac{5}{2}\)

5 phan 2

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

\(a,\frac{1}{2\times3}+\frac{1}{3\times4}+\frac{1}{4\times5}+\frac{1}{5\times6}=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}\)

\(=\frac{1}{2}-\frac{1}{6}=\frac{1}{3}\)

\(b,\left(1-\frac{1}{2}\right)\times\left(1-\frac{1}{3}\right)\times\left(1-\frac{1}{4}\right)=\frac{1}{2}\times\frac{2}{3}\times\frac{3}{4}\)

\(=\frac{1\times2\times3}{2\times3\times4}=\frac{1}{4}\)

=3/2*4/3*5/4...*11/10

=5,5

\(1\frac{1}{2}x1\frac{1}{3}:1\frac{1}{4}:1\frac{1}{5}\)

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

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

\(=\frac{4x4}{2x6}=\frac{2x2x4}{2x2x3}=\frac{4}{3}\)

\(1\frac{1}{2}\times1\frac{1}{3}\div1\frac{1}{4}\div1\frac{1}{5}=\frac{3}{2}\times\frac{4}{3}\div\frac{5}{4}\div\frac{6}{5}=\frac{3}{2}\times\frac{4}{3}\times\frac{4}{5}\times\frac{5}{6}\)

                                           \(=\frac{3\times4\times4\times5}{2\times3\times5\times6}=\frac{4}{3}\)

\(1\frac{1}{2}\times1\frac{1}{3}:1\frac{1}{4}:1\frac{1}{5}\)

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

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

\(=\frac{3\times4\times4\times5}{2\times3\times5\times6}\)

\(=\frac{4\times4}{2\times6}\)

\(=\frac{2\times2\times4}{2\times2\times3}\)

\(=\frac{4}{3}\)

_Chúc bạn học tốt_

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

\(\frac{1}{2}:\frac{3}{4}+\frac{1}{6}:\frac{3}{4}=\frac{3}{4}:\left(\frac{1}{2}+\frac{1}{6}\right)=\frac{3}{4}:\frac{2}{3}=\frac{9}{8}\)

\(\frac{2}{3}.\frac{4}{5}-\frac{1}{3}.\frac{4}{5}=\frac{4}{5}\left(\frac{2}{3}-\frac{1}{3}\right)=\frac{4}{5}.\frac{1}{3}=\frac{4}{15}\)

\(\frac{1}{2}:\frac{3}{4}-\frac{1}{6}:\frac{3}{4}=\frac{3}{4}:\left(\frac{1}{2}-\frac{1}{6}\right)=\frac{3}{4}:\frac{1}{3}=\frac{9}{4}\)

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

\(\frac{1}{2}:\frac{3}{4}+\frac{1}{6}:\frac{3}{4}=\frac{1}{2}.\frac{4}{3}+\frac{1}{6}.\frac{4}{3}=\left(\frac{1}{2}+\frac{1}{6}\right).\frac{4}{3}=\frac{2}{3}.\frac{4}{3}=\frac{8}{9}\)

c,d tương tự 

A) \(\frac{2}{3}\). \(\frac{4}{5}\)+ \(\frac{1}{3}\). \(\frac{4}{5}\)    B) \(\frac{1}{2}\). \(\frac{4}{5}\)+ \(\frac{1}{6}\): \(\frac{3}{4}\)      C) \(\frac{2}{3}\). \(\frac{4}{5}\)- \(\frac{1}{3}\). \(\frac{4}{5}\)         

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

= 1 . \(\frac{4}{5}\)                                   = \(\frac{28}{45}\)                                   = \(\frac{1}{3}\). 0

= \(\frac{4}{5}\)                                                                                         = 0

cái này khó quá nâng cao à

khó quá vậy giống nâng cao

\(=\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+....+\frac{1}{55}=\frac{2}{6}+\frac{2}{12}+\frac{2}{20}+....+\frac{2}{110}=2\times\left(\frac{1}{2\times3}+\frac{1}{3\times4}+\frac{1}{4\times5}+...+\frac{1}{10\times11}\right)\)

\(=2\times\left(\frac{1}{2}-\frac{1}{11}\right)=1-\frac{2}{11}=\frac{9}{11}\)

\(x\)là dấu nhân hả bạn? Nếu vậy thì mk làm cho nhé

\(A=\left(1-\frac{1}{2}\right)\cdot\left(1-\frac{1}{3}\right)\cdot\left(1-\frac{1}{4}\right)\cdot....\cdot\left(1-\frac{1}{20}\right)\)

\(A=\frac{1}{2}\cdot\frac{2}{3}\cdot\frac{3}{4}\cdot.......\cdot\frac{17}{18}\cdot\frac{18}{19}\cdot\frac{19}{20}=\frac{1}{20}\)

Vậy \(A=\frac{1}{20}\)

\(B=1\frac{1}{2}\cdot1\frac{1}{3}\cdot1\frac{1}{4}\cdot........\cdot1\frac{1}{2005}\cdot1\frac{1}{2006}\cdot1\frac{1}{2007}\)

\(B=\frac{3}{2}\cdot\frac{4}{3}\cdot\frac{5}{4}\cdot......\cdot\frac{2006}{2005}\cdot\frac{2007}{2006}\cdot\frac{2008}{2007}=\frac{2008}{2}=1004\)

Vậy \(B=1004\)

DẤU CHẤM LÀ DẤU NHÂN

a, 

\(=\frac{1}{2}.\frac{2}{3}.\frac{3}{4}....\frac{19}{20}=\frac{1}{20}\)

b, \(1\frac{1}{2}.1\frac{1}{3}....1\frac{1}{2017}=\frac{3}{2}.\frac{4}{3}....\frac{2018}{2017}=\frac{2018}{2}=1009\)

(1 - 1/2) x (1 - 1/3) x (1 - 1/4) x (1 - 1/5) x (1 - 1/6)

= 1/2 x 2/3 x 3/4 x 4/5 x 5/6

= 1/6 (tử và mẫu triệt tiêu cho nhau)

Đáp số : \(\frac{1}{5}\)

Tk mk mk tk lại ! ^^ 

= 1/2 x 2/3 x 3/4 x4/5

= 1x2x3x4/ 2x3x4x5 

=1/5

1\(\frac{1}{2}\)x 1\(\frac{1}{3}\)x 1\(\frac{1}{4}\)x 1\(\frac{1}{5}\)x 1\(\frac{1}{6}\)

= 3/2 x 4/3 x 5/4 x 6/5 x 7/6 

= 3.5