Canonical forms, rank and signature of three quadratic forms

Reduce the following quadratic forms to the canonical form and determine the rank and the signature:

1. \(x_1^2 + 2\sum_{i=2}^{n} x_i^2 - 2\sum_{i=1}^{n-1} x_i x_{i+1}\),

2. \(\sum_{i=1}^{n} x_i^2 + \sum_{1 \leqslant i < j \leqslant n} x_i x_j\),

3. \(\sum_{1 \leqslant i < j \leqslant n} x_i x_j\).