Linear Algebra Module Question:

5. [a] Find all r1,,31 ma E R such that the matrix :55 1.3 '1' _ 1 A CE : 6 1 {1 .13 :35 is orthogonal. [1D] {la} Let A E Mat(n?]R] he an orthogonal matrix. Prove that A\" = In if and only if A is skewsyrnmetrio. [5]