首先等比数列an中 有命题：m+n=k+h 则 aman=akah
于是 a1*a10=a2*a9=a3*a8=.=a5*a6=25
对数运算法则：log(ab)=log(a)+log(b)
log(a)表示以m为底,a的对数,
所以
log以5为底a1的对数+log以5为底a2的对数……+log以5为底a10
=log[a1a2a3.*a10]
=log[(a1a10)(a2a9)(a3a8)(a4a7)(a5a6)]
=log[25^5]
=log[5^10]
=10