Đặt
\(A=\frac{5}{2.7}+\frac{5}{7.12}+\frac{5}{12.17}+\frac{5}{17.22}+\frac{5}{22.27}+\frac{5}{27.32}+\frac{5}{32.37}\)
\(A=\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{12}+\frac{1}{12}-\frac{1}{17}+\frac{1}{17}-\frac{1}{22}+\frac{1}{22}-\frac{1}{27}+\frac{1}{27}-\frac{1}{32}+\frac{1}{32}-\frac{1}{37}\)
\(A=\frac{1}{2}-\frac{1}{37}=\frac{35}{74}\)
\(=\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{12}+\frac{1}{12}-\frac{1}{17}+...+\frac{1}{32}-\frac{1}{37}\)
\(=\frac{1}{2}-\frac{1}{37}\)
\(=\frac{37}{74}-\frac{2}{74}=\frac{35}{74}\)
\(=\frac{1}{2}.\frac{1}{7}+\frac{1}{7}.\frac{1}{12}...+\frac{1}{32}.\frac{1}{37}\)
= \(\frac{1}{2}+\frac{1}{37}\)
= \(\frac{37}{74}+\frac{2}{74}\)
\(\frac{39}{74}\)
tíck mik nha, mik nhanh nhất
= \(\frac{1}{2}\)- \(\frac{1}{7}\)+ \(\frac{1}{7}\)- \(\frac{1}{12}\)+ \(\frac{1}{12}\)- \(\frac{1}{17}\)+ \(\frac{1}{17}\)- \(\frac{1}{22}\)+ \(\frac{1}{22}\)- \(\frac{1}{27}\) + \(\frac{1}{27}\)- \(\frac{1}{32}\)+ \(\frac{1}{32}\)- \(\frac{1}{37}\)
= \(\frac{1}{2}\)- \(\frac{1}{37}\)
= \(\frac{35}{74}\)
\(=\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{12}+...\frac{1}{32}-\frac{1}{37}\)\(=\frac{1}{2}-\frac{1}{37}\)\(=\frac{35}{74}\)
Shujirin trả lời nhanh nhất nhưng mà sai hoàn toàn
Mà sao mọi người trả lời mà ko viết cả đề vào
Cho nên mình sẽ tích cho Nguyễn Quốc Việt
