Question #44f58

1 Answer
Jan 7, 2017

log(7/5)log(75)

Explanation:

x^7-1=(x-1)(1+x+x^2+cdots+x^6)x71=(x1)(1+x+x2++x6)
x^5-1=(x-1)(1+x+x^2+cdots+x^4)x51=(x1)(1+x+x2++x4)

so

(x^7-1)/(x^5-1)=(1+x+x^2+cdots+x^6)/(1+x+x^2+cdots+x^4)x71x51=1+x+x2++x61+x+x2++x4

then

lim_(x->1)log((x^7-1)/(x^5-1))=log(lim_(x->1)(1+x+x^2+cdots+x^6)/(1+x+x^2+cdots+x^4))=log(7/5)