# Math Help - Determine if the matrice are orthogonal

1. ## Determine if the matrice are orthogonal

Let A and B be orthogonal nxn matrices. Determine which of the following matrices are orthogonal. (Jusitify)

1) $A^{-1}$ 2) A - B
If AC is also an orthogonal nxn matrix, must C be orthogonal?

2. What is the definition of "orthogonal matrix"? Can you use that?