tui chỉ làm phần b thôi há !

B=\(\frac{3}{4}\)+\(\frac{27}{28}\)+\(\frac{69}{70}\)+...+\(\frac{867}{868}\)=\(\frac{4-1}{4}\)+\(\frac{28-1}{28}\)+\(\frac{70-1}{70}\)+...+\(\frac{868-1}{868}\)

= 1+1+..+1 -(\(\frac{1}{4}\)+\(\frac{1}{28}\)+\(\frac{1}{70}\)+...+\(\frac{1}{868}\)) = 10 - \(\frac{1}{3}\)(\(\frac{3}{1.4}\)+\(\frac{3}{4.7}\)+\(\frac{3}{7.10}\)+...+\(\frac{3}{28.31}\))

=10-\(\frac{1}{3}\)(1-\(\frac{1}{4}\)+\(\frac{1}{4}\)-\(\frac{1}{7}\)+\(\frac{1}{7}\)-\(\frac{1}{10}\)+...+\(\frac{1}{28}\)-\(\frac{1}{30}\))=10-\(\frac{1}{3}\)(1-\(\frac{1}{30}\))=10-\(\frac{1}{3}\).\(\frac{29}{30}\)=10-\(\frac{29}{30}\)=\(\frac{271}{30}\)

=\(\frac{1}{3}\times\left(\frac{2}{1}-\frac{2}{4}+\frac{2}{4}-\frac{2}{8}+...+\frac{2}{28}-\frac{2}{31}\right)\)

=\(\frac{1}{3}\times\left(\frac{2}{1}-\frac{2}{31}\right)=\frac{20}{31}\)

Bấm đúng cho tui, đi mà. CHÚC BẠN HỌC GIỎI

bài giải đó là sai giả như vầy nè

\(=\frac{1}{3}\cdot2\cdot\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{8}+...+\frac{1}{28}-\frac{1}{31}\right)\)

\(=\frac{2}{3}\left(1-\frac{1}{31}\right)\)

=\(\frac{2}{3}\cdot\frac{30}{31}=\frac{20}{31}\)

Trả lời

3/1.4+3/4.7+3/7.10

=3/1.3/10

=3/10

Chúc bạn học tốt #

\(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}\)

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

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

\(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}\)

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

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

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

tớ ko biết

S = 3 - \(\frac{3}{100}\)= \(\frac{300}{100}-\frac{3}{100}=\frac{297}{100}\)

S=3/1.4+3/4.7+3/7.10+.....+3/97.100

S=1/1-1/4+1/4-1/7+1/7-1/10+.....+1/97-1/100

S=1-1/100

S=99/100

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

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

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

Trả lời

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

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

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

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

#)Giải :

\(A=\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.11}+...+\frac{3}{97.100}\)

\(A=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+...+\frac{1}{97}-\frac{1}{100}\)

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

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

\(\frac{5}{1.4}+\frac{5}{4.7}+\frac{5}{7.10}+...+\frac{5}{100.103}\)

\(=\frac{5}{3}\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{100}-\frac{1}{103}\right)\)

\(=\frac{5}{3}\left(1-\frac{1}{103}\right)\)

\(=\frac{5}{3}.\frac{102}{103}=\frac{170}{103}\)

\(\frac{5}{1.4}+\frac{5}{4.7}+\frac{5}{7.10}+...+\frac{5}{100.103}=\frac{5}{3}.\left(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{100.103}\right)=\frac{5}{3}.\left(\frac{1}{1}-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{100}-\frac{1}{103}\right)=\frac{5}{3}.\left(\frac{1}{1}-\frac{1}{103}\right)=\frac{5}{3}.\frac{102}{103}=\frac{170}{103}\)

=5/3.(3/1.4+3/4.7+3/7.10+...+3/100.103)

=5/3.(1-1/4+1/4-1/7+1/7-1/10+...+1/100-1/103)

=5/3.(1-1/103)=5/3.102/103=170/103

                                       đáp số : 170/103

=1/1-1/4+1/4-1/7+1/7-1/10+...+1/40-1/41

=1-1/41=40/41

= 3(1/1.4+1/4.7+1/7.10+.......+1/40.43)

=3(1-1/4+1/4-1/7+1/7-1/10+....+1/40-1/43)

=3(1-1/43)

=3.42/43

=126/43

3/1.4+3/4.7+3/7.10+.....+3/40.43

=1/1-1/4+1/4-1/7+1/7-1/10+1/10-.....+1/40-1/43

=1+(-1/4+1/4)+(-1/7+1/7)+(-1/10+1/10)+.....-1/43

=1+0+0+0+....-1/43

1-1/43=43/43-1/43=42/43