Ta gọi A= 3/15+3/35+3/63+...+3/9603
A=3/3.5+3/5.7+3/7.9+...+3/97.99
2.A=3.2/3.5+3.2/5.7+...+3.2/97.99
2.A=3/3-3/5+3/5-3/7+...+3/97-3/99
2.A=3/3-3/99
2.A=32/33
A=32/33:2
A=16/33
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