5^10+5^9+...+5^0
=1+5+5^2+...+5^10
=1×(5^11-1)/(5-1)
=(5^11-1)/4
Sn=a1(1-q^n)/(1-q)
其中Sn表示等比数列前n项之和,a1表示首项,q表示公比(q≠1)
于是
5^n+5^(n-1)+...+5^0 ( n∈N)
=1+5+5^2+...+5^(n-1)+5^n
=1×[5^(n+1)-1)]/(5-1) 从0到n是n+1项
=[5^(n+1)-1]/4
2^4+2^3+2^2+2^1+2^0
=1+2+2^2+2^3+2^4
=1×(1-2^5)/(1-2)
=(2^5-1)/(2-1)
=31