Sn=1-1/2 +1/4-1/8 +…（-1)^n*1/2^n
热心网友
Sn=1-1/2 +1/4-1/8 +…（-1)^n*1/2^n(1/2)*Sn = 1/2 - 1/4 +1/8 +...+(-1)^n*1/2^(n+1)两式相加得：(3/2)*Sn= 1 + (-1)^n*1/2^(n+1)所以 Sn= (2/3)*[1 + (-1)^n*1/2^(n+1)]
Sn=1-1/2 +1/4-1/8 +…（-1)^n*1/2^n
Sn=1-1/2 +1/4-1/8 +…（-1)^n*1/2^n(1/2)*Sn = 1/2 - 1/4 +1/8 +...+(-1)^n*1/2^(n+1)两式相加得：(3/2)*Sn= 1 + (-1)^n*1/2^(n+1)所以 Sn= (2/3)*[1 + (-1)^n*1/2^(n+1)]