Prove that A - I is nonsingular
22563
Units and Nilpotents
64747
If $A^m=I$ then A is Diagonalizable
31116
Matrix given by $a_{ij} = 1/(i+j)$ is non-singular.
67383
Prove that $G'$ is not planar.
69046
Proof of $\mathbb{Q}$ is not cyclic
37398
Proof that$ (a+A)\cap A=\varnothing$ if $A$ is countable
110944
Proving that $AB-BA=cI$ for nontrivial $c \in \mathbb{C}$
73807
Prove positive definiteness
57969
Prove that $0$ is not an essential singularity (UW Madison Qualifying exam)
28003
How to prove $A+ A^T$ symmetric, $A-A^T$ skew-symmetric.
79727
Direct proof of non-flatness
139288
Formal proof that $e^x$ is not algebraic
42809
How can we show that $(I-A)$ is invertible?
72046
Prove all eigenvalues of $A^*A$ are non-negative
27775
Proving a function is not a contraction
101320
How to tell $i$ from $-i$?
13162
Prove $\alpha \in R[[x]]$ is a unit iff $a_0 \in R$ is a unit