# 2012-3 Integral

Compute $f(x)= \int_{0}^1 \frac{\log (1- 2t\cos x + t^2) }{t} dt.$

GD Star Rating
Let n be a positive integer and let Sn be the set of all permutations on {1,2,…,n}. Assume $$x_1+x_2 +\cdots +x_n =0$$ and $$\sum_{i\in A} x_i\neq 0$$ for all nonempty proper subsets A of {1,2,…,n}. Find all possible values of$\sum_{\pi \in S_n } \frac{1}{x_{\pi(1)}} \frac{1}{x_{\pi(1)}+x_{\pi(2)}}\cdots \frac{1}{x_{\pi(1)}+\cdots+ x_{\pi(n-1)}}.$