Show that if $a = a^{-1}$ then $a=1$ or $a=-1$
6128
If $a \cdot a = 1$ then $a = 1$ or $a = -1$
32929
Questions about proving $\lnot \lnot a = a$
156541
$a^b > b^a$ or $a^b b$ where $a,b$ are positive real numbers
6012
Prove that $\gcd(a^n - 1, a^m - 1) = a^{\gcd(n, m)} - 1$
111515
Proving that $-a=(-1)\cdot a$
83662
Prove that $ a $ divides $1^{a^{n}} + 2^{a^{n}} + ... + (a-1)^{a^{n}}$?
33030
Proof that $\inf A = -\sup(-A)$
110826
prove that : $ i = \sqrt {-1}\ $
15104
Show that $\big|\frac{a-b}{1-\overline{a}b}\big|=1$, when either $|a|=1$ or $|b|=1$.
154327
$A^2X = X$ show that $AX = X$, if $A_{ij} > 0$ and $x_{i} > 0$
1448
$x^a - 1$ divides $x^b - 1$ if and only if $a$ divides $b$
126018
Show that $ e^{A+B}=e^A e^B$
84283
If $a\neq 1$, find $(a+1)(a^2+1)(a^4+1)\ldots(a^{2^n}+1)$.
43834
Simple Complex Number Problem: $1 = -1$
37252
How can I show that $\begin{pmatrix} 1 & 1 \\ 0 & 1\end{pmatrix}^n = \begin{pmatrix} 1 & n \\ 0 & 1\end{pmatrix}$?
129564
Show that $A$ is an invertible matrix if $\left(A+I\right)^3=0$ and find $A^{-1}$
154133
Flawed proof by induction that $a^{n-1}=1$