Gọi biểu thức là A
A=1+1/2+1/4+1/8+...+1/1024
2A=2(1+1/2+1/4+1/8+...+1/1024)
2A=2+ 2.1/2 + 2.1/4 + 2.1/8+....+2.1/1024
2A=2+1+1/2+1/4+1/8+...+1/512
2A - A= (2+1+1/2+1/4+1/8+...+1/512)-(1+1/2+1/4+1/8+...+1/1024)
A=2- 1/1024 = 2047/1024
Cho ci 5s và ctlhn nhé e!!!