已知等比数列{an}的前三项是1√22若an=8√2则等于多少

已知等比数列{an}的前三项是1,√2,2,若an=8√2,则等于多少? 已知等比数列{an}的前三项是1,√2,2,若an=8√2,则等于多少?
(过程详细些~谢谢)   

参考案 a1 = 1, a2 = sqrt(2), a3 = 2;
q = a2/a1 = sqrt(2);

an = a1*q^(n-1);

n = 1 + logq(an/a1)
= 1 + log(an/a1)/log(q)
= 1+ log(8sqrt(2))/log(sqrt(2))
= 1+ 7
= 8.