S= 3/5.7 + 3/7.9 +...........................+3/59.61

  =3/2.(1/5 - 1/7 +1/7 -1/9 +....................+ 1/59-1/61)

  =3/2.(1/5-1/61)

              mình chỉ làm được tới đó

\(=\frac{1}{5}-\frac{1}{61}\)

\(=\frac{56}{305}\)

đã ns mk nhầm đừng k sai mk mak!>.<!

= 3(1/5.7+1/7.9+...+1/59.61)

= 3/2(2/5.7+2/7.9+...+2/59.61)

= 3/2(1-1/5+1/5-1/7+1/7-1/9+...+1/59-1/61)

= 3/2(1-1/61)=3/2.60/61=90/61

Chẳng biết mk làm đúng ko nữa!

\(\frac{3}{5.7}+\frac{3}{7.9}+...+\frac{3}{59.61}=\frac{3}{2}\cdot\left(\frac{2}{5.7}+\frac{2}{7.9}+...+\frac{2}{59.61}\right)=\frac{3}{2}\cdot\left(\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{59}-\frac{1}{61}\right)=\frac{3}{2}\cdot\left(\frac{1}{5}-\frac{1}{61}\right)=\frac{84}{305}\)

84/305 nha bạn

mk nha có cần giải ra ko

gọi biểu thức trên là A

gọi biểu thức trên là A. ta có: 

3A = 1/5.7+1/7.9+......+ 1/59.61

3A = 1/5-1/7+1/7-1/9+....+1/59-1/61

3A = 1/5 - 1/61

3A = 56/305

A = 56/305 : 3 = 56/915

dell btt

\(M=\frac{3}{5\cdot7}+\frac{3}{7\cdot9}+...+\frac{3}{59\cdot61}\)

\(M=\frac{3}{2}\left[\frac{2}{5\cdot7}+\frac{2}{7\cdot9}+...+\frac{2}{59\cdot61}\right]\)

\(M=\frac{3}{2}\left[\frac{1}{5}-\frac{1}{7}+...+\frac{1}{59}-\frac{1}{61}\right]\)

\(M=\frac{3}{2}\left[\frac{1}{5}-\frac{1}{61}\right]\)

\(M=\frac{3}{2}\cdot\frac{56}{305}=\frac{84}{305}\)

M=\(\frac{3}{5.7}\)+\(\frac{3}{7.9}\)+\(\frac{3}{9.11}\)+......................+\(\frac{3}{59.61}\)

M= 2.\((\frac{3}{5.7}+\frac{3}{7.9}+\frac{3}{9.11}+...........+\frac{3}{59.61})\):2

M=3.\((\frac{2}{5.7}+\frac{2}{7.9}+\frac{2}{9.11}+...........+\frac{2}{59.61})\):2

M=3.\((\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}+........+\frac{1}{59}-\frac{1}{61})\):2

M=3,\((\frac{1}{5}-\frac{1}{61})\):2

M=3.\(\frac{56}{305}\):2

M=\(\frac{168}{305}\):2

M=\(\frac{84}{305}\)

.Cho P=3/5.7+3/7.9+...+3/59.61=3/2.(1/5-1/61)=3/2.56/305=84/305 
 

bài này trong sách giáo khoa chương trình Vnen

thanksTuấn Anh Phan Nguyễn

84/305

 cần mk giải ko 

nhớ mk nha

Đặt \(A=\frac{3}{5.7}+\frac{3}{7.9}+...+\frac{3}{59.61}\)

\(\Rightarrow A=\frac{3}{2}.\left(\frac{2}{5.7}+\frac{2}{7.9}+...+\frac{2}{59.61}\right)=\frac{3}{2}.\left(\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{59}-\frac{1}{61}\right)\)

\(=\frac{3}{2}.\left(\frac{1}{5}-\frac{1}{61}\right)=\frac{3}{2}.\frac{56}{305}=\frac{84}{305}\)