Showing that $i$ is neither negative nor positive
71566
Positive and negative complex numbers?
67820
Showing that $(A_{ij})=\left(\frac1{1+x_i+x_j}\right)$ is positive semidefinite
69833
Number of elements not equal to their inverses is even number
132386
Show that $(\mathbb{Q}^*,\cdot)$ and $(\mathbb{R}^*,\cdot)$ aren't cyclic
143113
Non-inductive, not combinatorial proof of $\sum_{i \mathop = 0}^n \binom n i^2 = \binom {2 n} n$
17928
How to prove the following expression does not depend on x?
2408
Show that a polynomial has at least one positive solution/root.
57543
Show that a matrix is nilpotent.
102553
How to show that $f(z) = f(i)$
36011
Show that the product of two consecutive natural numbers is never a square.
48314
Show that if a function is not negative and its integral is $0$ than the function is $0$
106398
If $A$ is invertible show that $\det(A) \neq 0$
31116
Matrix given by $a_{ij} = 1/(i+j)$ is non-singular.
66104
Showing that something is a sufficient statistic
110944
Proving that $AB-BA=cI$ for nontrivial $c \in \mathbb{C}$
46698
Showing a set is closed under inverses
156669
Trying to prove a simple (?) inequality