3/1+6/1+12/1+24/1+48/1+96/1+192/1+384/1等于多少
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a1= 1/3
an = (1/2)a(n-1)
an = (1/2)^(n-1) .a1
= (1/3)(1/2)^(n-1)
Sn = a1+a2+...+an
= (2/3) ( 1- (1/2)^n )
1/3+1/6+1/12+1/24+1/48+1/96+1/192+1/384
= S8
=(2/3) ( 1- (1/2)^8 )
= 255/384
an = (1/2)a(n-1)
an = (1/2)^(n-1) .a1
= (1/3)(1/2)^(n-1)
Sn = a1+a2+...+an
= (2/3) ( 1- (1/2)^n )
1/3+1/6+1/12+1/24+1/48+1/96+1/192+1/384
= S8
=(2/3) ( 1- (1/2)^8 )
= 255/384
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