\(A=\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+...+\frac{1}{256}+\frac{1}{512}\)
\(A\cdot2=1+\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+...+\frac{1}{256}\)
\(A\cdot2-A=1-\frac{1}{512}\)
\(A=\frac{511}{512}\)
1/2+1/4+1/8+1/16+...+1/256+1/512(gọi A là tổng các PS trên)
A*2=(1+1/2+1/4+1/8+...+1/128+1/256)/2
A*2-A=1+1/2+1/4+1/8+...+1/128+1/256-1/2-1/4-1/8-1/16-...-1/256-1/512.
A=1-1/512
A=511/512.
Kết bạn với mình nha!