Đặt \(A=\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}+\frac{1}{32}+\frac{1}{64}\)
\(2A=1+\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}+\frac{1}{32}\)
\(2A-A=\left(1+\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}+\frac{1}{32}\right)-\left(\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}+\frac{1}{32}+\frac{1}{64}\right)\)
\(A=1-\frac{1}{64}\)
\(A=\frac{63}{64}\)
=32/64+14/64+8/64+4/64+2/64+1/64
=32+14+8+4+2+1/64
=61/64
1/2 +1/4+ 1/8+1/16+1/32+1/64
=1/1×2+1/2×2+1/2×4+1/4×4+1/4+8+1/8×8
=1/1-1/2+1/2-1/2+1/2-1/4+1/4-1/4+1/4-1/8+1/8-1/8
=1-1/8
=7/8
1/2 + 1/4 + 1/8 + 1/16 + 1/32 + 1/64
=0.984375
tính nhanh p/s 1+ 5/4 + 5/8 + 5/16 + 5/32 + 5/64
