Đáp án:
Giải thích các bước giải:
gọi A=1/2+1/4+1/8+1/16+1/32+...+1/512+1/1024
2xA=1/2+1/4+...+1/512
2xA-A=(1/2+1/4+...+1/512)-(1/2+1/4+1/8+1/16+1/32+...+1/512+1/1024)
A=1-1/1024
A=1023/1024
VẬY A=1023/1024
b,1/15+1/35+1/63+1/99
=1/2(2/3×5+2/5×7+2/7×9+2/9.11)
=1/2(1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11)
=1/2[1/3+(-1/5+1/5)+-(1/7+1/7)+(-1/9+1/9)-1/11]
=1/2(1/3-1/11)
=1/2×8/33
=4/33
