= 1 - 1/3 + 1/3 - 1/5 + 1/5 - 1/7 +....... + 1/97 - 1/99
= 1- 1/99
= 98/99
Mãi yêu chàng trai Song Tử:bạn làm vầy là ngu roày
3/1.3+3/3.5+3/5.7+....+3/97.99=98/99
= 1 - 1/3 + 1/3 - 1/5 + 1/5 - 1/7 + ......... + 1/97 - 1/99.
= 1 - 1/99
= 98/99.
Ai tích mik mik sẽ tích lại nha !
Đặt A=3/1.3+3/3.5+3/5.7+....+3/97.99
\(=\frac{3}{2}\left(\frac{3}{1\cdot3}+\frac{3}{3\cdot5}+...+\frac{3}{97\cdot99}\right)\)
\(=\frac{3}{2}\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{97}-\frac{1}{99}\right)\)
\(=\frac{3}{2}\left(1-\frac{1}{99}\right)\)
\(=\frac{3}{2}\cdot\frac{98}{99}\)
\(=1\frac{16}{33}\)
\(\dfrac{3}{1\cdot3}+\dfrac{3}{3\cdot5}+\dfrac{3}{5\cdot7}+...+\dfrac{3}{97\cdot99}\\ =\dfrac{3}{2}\cdot\left(\dfrac{1}{1}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+...+\dfrac{1}{97}-\dfrac{1}{99}\right)\\ =\dfrac{3}{2}\cdot\left(\dfrac{1}{1}-\dfrac{1}{99}\right)\\ =\dfrac{3}{2}\cdot\dfrac{98}{99}=\dfrac{49}{33}\)