2+2∧3+2∧5+2∧7+2∧9+………+2∧(n-1)=?
问题描述:
2+2∧3+2∧5+2∧7+2∧9+………+2∧(n-1)=?
答
这个是等等比数列求和,a1是首项,n是项数a1=2an=2^(n-1)一共有n+1/2项公比q=2^2=4利用等比数列求和公式S=a1(1-q^n)/(1-q)带入即可得到S=2+2^3+2^5+……+2^(n-1) =2(1-4^[(n+1)/2])/(1-4)=-2(1-4^[(n+1)/2])/3=[2*...