Projection matrix that sum to identity are orthogonal
69474
Orthogonal projections with $\sum P_i =I$, proving that $i\ne j \Rightarrow  P_{j}P_{i}=0$
55031
Show any matrix $A_{n\times n}$ can be written as sum of two nonsingular matrices
136698
Why are there different ways of building projection matrices?
108505
Matrix Concentration for Products- Orthogonality Property
52946
If $X$ is an orthogonal matrix, why does $X^TX = I$?
47589
Product of a primitive matrix and its transpose.
128835
Compactness of the set of $n \times n$ orthogonal matrices
124095
$A$ is a real orthogonal matrix, prove that $ (I+A)^{-1}(I-A)$ is skew-symmetric
111769
Why is inverse of orthogonal matrix is its transpose?
84522
A better proof for $\det(P) = \pm1$ if $P$ is an orthogonal matrix
146099
Why is this true: The only orthogonal projection that is also unitary from $\Bbb C^n$ to $\Bbb C^n$ is the identity
123044
Commutative matrices are multiples of the identity
30877
How to show that the set of orthogonal n x n matrices forms a group under multiplication
13442
Find three real orthogonal matrices of order $3$ having all integer entries.
112353
Prove that all 2x2 orthogonal matrices can be expressed as Rotation or Reflection
147903
Similar matrices-Identity
34043
A rank-one matrix is the product of two vectors