等比数列求和
n+1项
2^0,2^1,...,2^n
这是一个等比数列,a1=1, q=2 , an= a1.q^(n-1) = 2^(n-1)
2^0+2^1+...+2^n
这是 2^0+2^1+...+2^n =a1+a2+...+a(n+1) =S(n+1) = a1.(q^(n+1) -1)/(q-1)
=(2^(n+1) -1)/(2-1)
化简
=2^(n+1) -1
故得出
2^0+2^1+...+2^n =2^(n+1) -1
2^0+2^1+……+2^n
=〔1*(1-2^(n+1))〕/(1-2)
=-(1-2*2^n)
=2*2^n-1