Why $(-1)\cdot (-1)=1$
17515
Why is negative times negative = positive?
40534
What is $(-1)^{\frac{2}{3}}$?
119759
Help ending a proof using binomial theorem: $\sum_{k=0}^n {n \choose k}\cdot\frac{(-1)^k}{k+1} = \frac{1}{n+1}$
107390
Why is (-1)(-1) = 1?
158862
Show that $a(-1) = (-1)a = -a $.
6650
Why $\sqrt{-1 \times -1} \neq \sqrt{-1}^2$?
126672
Product of principal ideals: $(a)\cdot (b) = (a b)$
57780
$\sum_{i=1}^n i\cdot i! = (n+1)!-1$ By Induction
103061
Why is it true that $\mathrm{adj}(A)A = \det(A) \cdot I$?
132386
Show that $(\mathbb{Q}^*,\cdot)$ and $(\mathbb{R}^*,\cdot)$ aren't cyclic
156235
Are $x \cdot 0 = 0$, $x \cdot 1 = x$, and $-(-x) = x$ axioms?
19962
Why is $\infty \cdot 0$ not clearly equal to $0$?
122330
Prove that there exists some $c\in(-3,3)$ such that$ \ \ g(c) \cdot g''(c)<0$.
34299
Combinatorial proof of $\sum_{k=0}^n k \cdot k! = (n+1)! -1$
81875
why is $\sqrt{-1} = i$ and not $\pm i$?
88334
Why is the expression $\underbrace{n\cdot n\cdot \ldots n}_{k \text{ times}}$ bad?
68848
How to simplify $\sum_{k=1}^nk\cdot k!$