\(A=\dfrac{1}{2}+\dfrac{1}{2^2}+\dfrac{1}{2^3}+...+\dfrac{1}{2^9}\\ 2A=1+\dfrac{1}{2}+\dfrac{1}{2^2}+...+\dfrac{1}{2^8}\\ 2A-A=\left(1+\dfrac{1}{2}+...+\dfrac{1}{2^8}\right)-\left(\dfrac{1}{2}+\dfrac{1}{2^2}+...+\dfrac{1}{2^9}\right)\\ A=1-\dfrac{1}{2^9}=\dfrac{511}{512}\)
(1/2+1/4+1/8.....+1/256+1/512)*2=511/256
Tính nhanh tổng A biết :A =1/2+1/4+1/8+1/16+....+1/256+1/512
1/2+1/4+1/8+1/16+...+1/256+1/512
1/2 + 1/4 + 1/8 + 1/16 +...+ 1/256 + 1/512
1/2+1/4+1/8+1/16+........+1/256+1/512
A=1/2+1/4+1/8 + 1/16+1/32+1/64+1/128+1/256+1/512+1/1024 = ?
a)1/2+1/6+1/12+........+1/9900+1/10100
b)1/2+1/4+1/8+....+1/256+1/512
a)1/2+1/6+1/12+.........+1/9900+1/10100 = ?
b)1/2+1/4+1/8+...........+1/256+1/512 = ?
Tính tổng S = 1/2+1/4+1/8+.......+1/256+1/512
