数学,判断log(an,an+1)-log(an-1,an)的符号,要过程 ｛an｝等比 +1 -1均为下标

log(an,an+1)中an是底数?
log(an,an+1)-log(an-1,an)=lg(an+1)l/g(an)-lg(an)/lg(an-1)
设等比是k
所以an+1=k*an.an=k*an-1
log(an,an+1)-log(an-1,an)=lg(an+1)/lg(an)-lg(an)/lg(an-1)
=lg(k*an)/lg(an)-lg(k*an-1)/lg(an-1)
=(lg(k)+lg(an))/lg(an)-(lg(k)+lg(an-1))/lg(an-1)
=lg(k)*(1/lg(an)-1/lg(an-1))
当k>1时an>an-1
原式

log(an,an+1)这个中间的是加号，还是减号啊？以减号为例：
log(an-an+1)-log(an-1-an)=log(an-an+1/an-1-an),设{an}的公比为q（q不等于1）
则log(an-an+1)-log(an-1-an)=log（q），所以要依q的情况判断，
如果q>1,则logq>0;如果0希望对你有帮助！