\(A=\frac{3}{2}\left(\frac{2}{5.7}+\frac{2}{7.9}+...+\frac{2}{59.61}\right)\)

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

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

\(\Rightarrow A=\frac{3}{2}.\left(\frac{2}{5.7}+\frac{2}{7.9}+....+\frac{2}{59.61}\right)\)

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

\(\Rightarrow A=\frac{3}{2}.\left(\frac{1}{5}-\frac{1}{61}\right)\)

\(\Rightarrow A=\frac{3}{2}.\frac{56}{305}\)

\(\Rightarrow A=\frac{84}{305}\)

=> A= \(\frac{3}{2}\) .( \(\frac{1}{5}\) - \(\frac{1}{7}\) + \(\frac{1}{7}\) - \(\frac{1}{9}\) +...+ \(\frac{1}{59}\) - \(\frac{1}{61}\))

=> A=\(\frac{3}{2}\) . (\(\frac{1}{5}\) - \(\frac{1}{61}\) ) => A= \(\frac{3}{2}\). \(\frac{56}{305}\) = \(\frac{84}{305}\) Vậy A= \(\frac{84}{305}\)

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

    \(=\frac{3}{2}.\left(\frac{2}{5.7}+\frac{2}{7.9}+...+\frac{2}{59.61}\right)\)

    \(=\frac{3}{2}.\left(\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{53}-\frac{1}{61}\right)\)

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

    \(=\frac{3}{2}.\frac{56}{305}\)

    \(=\frac{84}{305}\)

M=3.(\(\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-....+\frac{1}{59}-\frac{1}{60}\)\(\frac{1}{61}\))

M= 3.(\(\frac{1}{5}-\frac{1}{61}\))

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

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

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

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

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

\(\frac{2}{3}A=\frac{2}{3}.\left(\frac{3}{5.7}+\frac{3}{7.9}+...+\frac{3}{59.61}\right)\)

\(\frac{2}{3}A=\frac{2.3}{3.5.7}+\frac{2.3}{3.7.9}+...+\frac{2.3}{3.59.61}\)

\(\frac{2}{3}A=\frac{2}{5.7}+\frac{2}{7.9}+...+\frac{2}{59.61}\)

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

\(\frac{2}{3}A=\frac{1}{5}-\frac{1}{61}\)

\(\frac{2}{3}A=\frac{56}{305}\)

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

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

dễ ợt

A= 1/5-1/61= 56/305

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

\(A=\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{3}{59.61}\)

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

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

BÀi này dễ thôi bạn ạ 

N=3(1/5.7+1/7.9+.........+1/197.199)

N=3/2( 1/5-1/7+1/7-1/9+1/9-..........+1/197-1/199)

N=3/2(1/5-1/199)

N=3/2.194/995

N=291/995

k đúng cho mình nhé

N=3.1/2.(1/5-1/7+1/7-1/9+1/9-1/11+...+1/197-1/199)

N=3.1/2.(1/5-1/99)

N=3.1/2.94/495

N=3.47/495

N=47/165

N=3/5.7+3/7.9+........+3/197.199

=>N=3/2(2/5.7+2/7.9+.....+2/197.199)

=>N=3/2(1/5-1/7+1/7-1/9+........+1/197-1/199)

=>N=3/2(1/5-1/199)

=>N=3/2x194/995=291/995

k mình nha

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

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

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

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

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

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

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

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

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

Đặt A=như đã cho.

=>1/2A=2/5*7+2/7*9+2/9*11+...+2/59*61.

=>1/2A=1/5-1/7+1/7-1/9+1/9-1/11+...+1/59-1/61.

=>1/2A=1/5-1/61=56/305.

=>A=56/305*2=112/305.

k nha đúng đó.Có j kb nha.

pn kia nhầm zùi

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