Đặt A=3/2+3/8+...+3/512
bn tách
3/2=3/2^1
3/8=3/2^3
....
3/512=3/2^9
Rồi nhân nó lên trừ đc bao nhiêu - đi A ban đầu là đc
Chúc bạn học tốt
=768/512+192/512+48/512+12/512+3/512
=768+192+48+12+3/512
=1023/512
(\(\frac{3}{2}\) + \(\frac{3}{8}\) ) + ( \(\frac{3}{32}\) + \(\frac{3}{128}\) ) + \(\frac{3}{512}\)
= ( \(\frac{15}{8}\) + \(\frac{15}{128}\) ) + \(\frac{3}{512}\)
= \(\frac{255}{128}\) + \(\frac{3}{512}\)
= \(\frac{1023}{512}\)
=768/512+192/512+48/512+12/512+3/512
=768+192+48+12+3/512
=1023/512