A=\(\frac{1}{4.7}+\frac{1}{7.10}+\frac{1}{10.13}+...+\frac{1}{73.76}\)

3A=3(\(\frac{1}{4.7}+\frac{1}{7.10}+\frac{1}{10.13}+...+\frac{1}{73.76}\))

3A=\(\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+...+\frac{3}{73.76}\)

3A=\(\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+...+\frac{1}{73}+\frac{1}{76}\)

3A=\(\frac{1}{4}-\frac{1}{76}\)

3A=\(\frac{9}{38}\)

A=\(\frac{9}{38}\):3

A=\(\frac{3}{38}\)

đặt A=1/4.7+1/7.10+...+1/73.76

3A=1/4-1/7+1/7-1/10+...+1/ 73 -1/ 76
 

\(A=\frac{1}{4.7}+\frac{1}{7.10}+\frac{1}{10.13}+...+\frac{1}{73.76}\)

\(3A=\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+...+\frac{3}{73.76}\)

\(3A=\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+...+\frac{1}{73}-\frac{1}{76}\)

\(3A=\frac{1}{4}-\frac{1}{76}\)

\(3A=\frac{9}{38}\)

\(A=\frac{3}{38}\)

các bn trả lời nhanh nhé

đến 9:10 nhé

\(A=\frac{2}{4.7}+\frac{2}{7.10}+\frac{2}{10.13}+.....+\frac{2}{73.76}\)

\(=\frac{2}{3}\left(\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+....+\frac{3}{73.76}\right)\)

\(=\frac{2}{3}\left(\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+....+\frac{1}{73}-\frac{1}{76}\right)\)

\(=\frac{2}{3}\left(\frac{1}{4}-\frac{1}{76}\right)\)

\(=\frac{2}{3}.\frac{9}{38}=\frac{3}{19}\)

A=\(\frac{3}{3}\cdot\left(\frac{2}{4\cdot7}+\frac{2}{7\cdot10}+\frac{2}{10\cdot13}+...+\frac{2}{73\cdot76}\right)\)

A=\(\frac{1}{3}\cdot3\cdot\left(\frac{2}{4\cdot7}+\frac{2}{7\cdot10}+\frac{2}{10\cdot13}+...+\frac{2}{73\cdot76}\right)\)

A=\(\frac{1}{3}\cdot\left(\frac{3}{4\cdot7}+\frac{3}{7\cdot10}+\frac{3}{10\cdot17}+...+\frac{3}{73\cdot76}\right)\)

A=\(\frac{1}{3}\cdot\left(\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}-\frac{1}{13}+...+\frac{1}{73}-\frac{1}{76}\right)\)

A=\(\frac{1}{3}\cdot\left(\frac{1}{4}-\frac{1}{76}\right)\)

A=\(\frac{1}{3}\cdot\left(\frac{19}{76}-\frac{1}{76}\right)\)

A=\(\frac{1}{3}\cdot\frac{18}{76}\)

A=\(\frac{1\cdot6}{1\cdot76}\)

A=\(\frac{6}{76}\)

chúc bạn một ngày tốt lành

3/4.7 + 3/7.10 + ...+ 3/73.76

=1/4 - 1/7 +1/7 - 1/10 + ... + 1/73 - 1/76 

=1/4 - 1/76 

=18/76 

=9/38 

\(\frac{3}{4x7}+\frac{3}{7x10}+.......+\frac{3}{73x76}\)

=\(\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{73}-\frac{1}{76}\)

\(=\frac{1}{4}-\frac{1}{76}\)

\(=\frac{9}{38}\)

                                      Đáp số :\(\frac{9}{38}\)

B=3/4.7+3/7.10+...+3/73.76

   =1/4.7+.1/7.10+...+1/73.76

   =1/4-1/7+1/7-1/10+...+1/73+1/76

   =1/4-1/76 

   =9/36

\(A=\frac{3^2}{1.4}+\frac{3^2}{4.7}+\frac{3^2}{7.10}+.....+\frac{3^2}{97.100}\)

\(=3\left(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+....+\frac{3}{97.100}\right)\)

Ta thấy :

 \(\frac{3}{1.4}=\frac{4-1}{1.4}=1-\frac{1}{4}\)

\(\frac{3}{4.7}=\frac{7-4}{4.7}=\frac{1}{4}-\frac{1}{7}\)

\(.........\)

\(\frac{3}{97.100}=\frac{100-97}{97.100}=\frac{1}{97}-\frac{1}{100}\)

\(\Rightarrow A=3\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+....+\frac{1}{97}-\frac{1}{100}\right)\)

\(=3\left(1-\frac{1}{100}\right)=3\cdot\frac{99}{100}=\frac{297}{100}\)

đáp án = \(\frac{297}{100}\)

đúng không?

kết bạn với mh nha

A:3=\(\frac{3}{1.4}+\frac{3}{4.7}\)\(+.....+\frac{3}{97.100}\)

A:3=\(\frac{1}{1}-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+....+\frac{1}{97}-\frac{1}{100}\)

A:3=\(\frac{1}{1}-\frac{1}{100}\)

A:3=\(\frac{99}{100}\)

A=\(\frac{99}{100}.3\)

A=\(\frac{297}{100}\)

\(A:3=\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+....+\frac{3}{97.100}\)

\(A:3=\left(\frac{1}{1}-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+...+\frac{1}{97}-\frac{1}{100}\right)\)

\(A:3=\frac{1}{1}-\frac{1}{100}\)

\(A:3=\frac{99}{100}\)

\(A=\frac{99}{100}.3\)

\(A=\frac{297}{100}\)

http://olm.vn/hoi-dap/question/772291.html

sau 3 phút có kết quả tùy bạn

A=\(\frac{37}{78}\)

B=\(\frac{9}{38}\)

a, 1/1.2+1/1.3+...+1/99.100

= 1-1/2+1/2-1/3+1/3+...+1/99-1/100

=1-1/100

=99/100

A = 99/100

B = 2014/6051

C = 99

D = 9/38

\(=>C=\frac{3}{4}-\frac{3}{7}+\frac{3}{7}-\frac{3}{10}+....+\frac{3}{73}-\frac{3}{76}\)

\(=>C=\frac{3}{4}-\frac{3}{76}\)

\(=>C=\frac{54}{76}\)

\(=>C=\frac{27}{38}\)

\(C=\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+....+\frac{3}{73.76}\)

=> Cộng vế với vế , ta được :

\(C=\frac{3}{3}\left(\frac{1}{4.7}+\frac{1}{7.10}+\frac{1}{10.13}+....+\frac{1}{73.76}\right)\)

 \(\Rightarrow C=1\left(\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+....+\frac{1}{73}-\frac{1}{76}\right)\)

 \(\Rightarrow C=1\left(\frac{1}{4}-\frac{1}{76}\right)\)

\(\Rightarrow C=1\left(\frac{19}{76}-\frac{1}{76}\right)=1\frac{18}{76}\)

\(\frac{3^2}{1.4}+\frac{3^2}{4.7}+\frac{3^2}{7.10}+\frac{3^2}{10.13}+...+\frac{3^2}{97.100}\)

\(=3.\left(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+...+\frac{3}{97.100}\right)\)

\(=3.\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{97}-\frac{1}{100}\right)\)

\(=3.\left(1-\frac{1}{100}\right)\)

\(=3.\frac{99}{100}\)