\(\frac{2}{3\times5}+\frac{2}{5\times7}+\frac{2}{7\times9}+.....+\frac{2}{97\times99}\)
\(=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+.....+\frac{1}{97}-\frac{1}{99}\)
\(=\frac{1}{3}-\frac{1}{99}\)
\(=\frac{33}{99}-\frac{1}{99}\)
\(=\frac{32}{99}\)
Chúc bạn học tốt
M=2/3.5+2/5.7+...+2/97.99
M=1.(1/3-1/5+...+1/97-1/99)
M=1.(1/3-1/99)
M=32/99
M=2/3*5+2/5*7+2/7*9+...+2/97*99
2/3*5=5-3/3*5=5/3*5-3/3*5=1/3-1/5
2/5*7=7-5/5*7=7/5*7-5/5*7=1/5-1/7
2/7*9=9-7/7*9=9/7*9-7/7*9=1/7-1/9
......
2/97*99=99-97/97*99=99/97*99-97/97*99=1/97-1/99
M=1/3-1/5+1/5-1/7+1/7-1/9+....+1/97-1/99= 1/3-1/99= 32/99
