Question

tính tổng S=\(\frac{2}{5.7}+\frac{2}{7.9}+...+\frac{2}{59.61}\)

Answer 1

\(=\frac{1}{5}-\frac{1}{61}=\frac{56}{305}\)

Answer 2

\(S=\frac{2}{5.7}+\frac{2}{7.9}+...+\frac{2}{59.61}\)

\(S=\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{59}-\frac{1}{61}\)

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

\(S=\frac{61}{305}-\frac{5}{305}\)

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

Answer 3

\(S=\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{59}-\frac{1}{61}\)

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

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

Answer 4

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

S=2.(1/5-1/61)

S=2.56/305

S=112/305

Answer 5

S =\(\frac{2}{5\cdot7}+\frac{2}{7\cdot9}+...+\frac{2}{59\cdot61}\) 

=\(2\left(\frac{1}{5\cdot7}+\frac{1}{7\cdot9}+...+\frac{1}{59\cdot61}\right)\)

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

=\(2\left(\frac{1}{5}-\frac{1}{61}\right)=2\left(\frac{61}{305}-\frac{5}{305}\right)\)

= \(2\frac{56}{305}=\frac{666}{305}\)

Chúc bn hk tốt !

Answer 6

nhầm \(2\frac{56}{305}=\frac{112}{305}\)

chúc bn hk tốt!

k mk nha, làm đầy đủ 

Answer 7

ACE....

sai quá sai luôn bạn  ơi

Answer 8

\(S=\frac{2}{5.7}+\frac{2}{7.9}+...+\frac{2}{59.61}\)

\(\Rightarrow\frac{1}{2}S=\frac{1}{5.7}+\frac{1}{7.9}+...+\frac{1}{59.61}\)

\(\Rightarrow\frac{1}{2}S=\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{59}-\frac{1}{61}\)

\(\Rightarrow\frac{1}{2}S=\frac{1}{5}-\frac{1}{61}\)

\(\Rightarrow\frac{1}{2}S=\frac{61}{305}-\frac{5}{305}\)

\(\Rightarrow\frac{1}{2}S=\frac{56}{305}\)

\(\Rightarrow S=\frac{56}{305}\div\frac{1}{2}\)

\(\Rightarrow S=\frac{56}{305}\times2\)

\(\Rightarrow S=\frac{112}{305}\)

Answer 9

thiếu \(\frac{1}{2}\)là sai bởi vì bài này đặt \(\frac{1}{2}\)ra mà

bn nào làm thiếu và có kết quả là \(\frac{56}{305}\)là sai

chúc bn hk tốt !