\(B=\frac{5.7}{2.7}+\frac{4.7}{7.11}+\frac{3.7}{11.14}+\frac{1.7}{14.15}+\frac{13.7}{15.28}\)

\(B=7.\left(\frac{5}{2.7}+\frac{4}{7.11}+\frac{3}{11.14}+\frac{1}{14.15}+\frac{13}{15.28}\right)\)

\(B=7\left(\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{1}{15}+\frac{1}{15}-\frac{1}{28}\right)\)

\(B=7\left(\frac{1}{2}-\frac{1}{28}\right)\)

\(B=7.\frac{13}{28}\)

\(B=\frac{13}{4}\)

uề

tiến y đan nhe 

hấn gửi câu hỏi là trả lời liền

còn choa gửi thì éo trả lời

Đặt \(A=\frac{5}{2.1}+\frac{4}{1.11}+\frac{3}{2.11}+\frac{1}{2.15}+\frac{13}{15.4}\)

\(\frac{1}{7}.A=\frac{5}{2.7}+\frac{4}{7.11}+\frac{3}{11.14}+\frac{1}{14.15}+\frac{13}{15.28}\)

\(\frac{1}{7}.A=\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{1}{15}+\frac{1}{15}-\frac{1}{28}\)

\(\frac{1}{7}.A=\frac{1}{2}-\frac{1}{28}\)

\(\frac{1}{7}.A=\frac{14}{28}-\frac{1}{28}=\frac{13}{28}\)

\(A=\frac{13}{28}:\frac{1}{7}=\frac{13}{28}.7=\frac{13}{4}\)

Phân số cuối chép sai đề rùi nhé!

thank you

Ta có

 \(\frac{1}{7}B=\frac{5}{2.7}+\frac{4}{7.11}+\frac{3}{11.14}+\frac{1}{14.15}+\frac{13}{15.28}\)

\(\Rightarrow\frac{1}{7}B=\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{1}{15}+\frac{1}{15}-\frac{1}{28}\)

\(\Rightarrow\frac{1}{7}B=\frac{1}{2}-\frac{1}{28}\)

\(\Rightarrow\frac{1}{7}B=\frac{13}{28}\)

\(\Rightarrow B=\frac{13}{4}\)

\(=\frac{5}{2.1}+\frac{4}{1.11}+\frac{3}{11.2}+\frac{1}{2.15}+\frac{13}{15.4}\)

B:7=\(\frac{5}{2.7}+\frac{4}{7.11}+\frac{3}{11.14}+\frac{1}{14.15}+\frac{13}{15.28}\)

B:7=\(\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+...+\frac{1}{15}-\frac{1}{28}\)

B:7=\(\frac{1}{2}-\frac{1}{28}\)=\(\frac{13}{28}\)=>B=\(\frac{13}{4}\)

B = \(\frac{5}{2.1}+\frac{4}{1.11}+\frac{3}{11.2}+\frac{1}{2.15}+\frac{13}{15.4}\)\(=7\left(\frac{5}{2.7}+\frac{4}{7.11}+\frac{3}{11.14}+\frac{1}{14.15}+\frac{13}{15.28}\right)\)\(=7\left(\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{1}{15}+\frac{1}{15}-\frac{1}{28}\right)\)

\(=7\left(\frac{1}{2}-\frac{1}{28}\right)=\frac{7}{2}-\frac{1}{4}=\frac{14}{4}-\frac{1}{4}=\frac{13}{4}\)

đề của tớ ngắn hơn bn nhiều

7 ở đâu vậy bn, mình ko hỉu lắm...

\(B=\frac{5}{2.1}+\frac{4}{1.11}+\frac{3}{11.2}+\frac{1}{2.15}+\frac{13}{15.4}\)

\(B=\frac{5}{2}+\frac{4}{11}+\frac{3}{22}+\frac{1}{30}+\frac{13}{60}\)

\(B=\left(\frac{5}{2}+\frac{4}{11}+\frac{3}{22}\right)+\left(\frac{1}{30}+\frac{13}{60}\right)\)

\(B=\frac{66}{22}+\frac{15}{60}\)

\(B=3+\frac{1}{4}\)

\(B=\frac{13}{4}\)

\(B=\frac{5}{2.1}+\frac{4}{1.11}+\frac{3}{11.2}+\frac{1}{2.15}+\frac{13}{15.4}\)

\(\frac{B}{7}=\frac{5}{2.7}+\frac{4}{7.11}+\frac{3}{11.14}+\frac{1}{14.15}+\frac{13}{15.4}\)

\(\frac{B}{7}=\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-...+\frac{1}{15}-\frac{1}{28}\)

\(\frac{B}{7}=\frac{1}{2}-\frac{1}{28}\)

\(\frac{B}{7}=\frac{13}{28}\)

\(B=\frac{13}{28}.7\)

\(B=\frac{13}{4}\)

B = 7(5/2.7 + 4/7.11 + 3/11.14 + 1/14.15 + 13/15.28)

B = 7.(1/2 - 1/7 + 1/7 - 1/11 + 1/11 - 1/14 + 1/14 - 1/15 + 1/15 - 1/28)

B = 7.( 1/2 - 1/28)

B = 7. 13/28

B = 13/4

k mk đi!

why! tại sao có thể làm như vậy

=7.(5/2.7+4/7.11+3/11.14+1/14.15+13/15.28)

=7.(1/2-1/7+1/7-1/14+1/14-1/15+1/15-1/28)

=7.(1/2-1/28)

=13/4

xin hãy trả lời

xin hãy trả lời

câu chả lời ở phần câu hỏi tương tự của son phan