Proof that $(-1)\cdot a=(-a)$
158862
Show that $a(-1) = (-1)a = -a $.
111298
Direct Proof that $1 + 3 + 5 + \cdots+ (2n - 1) = n\cdot n$
90496
Proving $\lim \frac{x^n-a^n}{x-a}=n\cdot a^{n-1}$
83753
Why $\,p \cdot (p^{-1} \mod q) + q \cdot (q^{-1} \mod p) = pq + 1$?
107765
Prove that there exists two roots in $[-1,1]$
6539
Prove $\sum_{i=1}^n i! \cdot i = (n+1)! - 1$?
30860
Prove that $f(x)=0$ in $[-1,1]$.
34299
Combinatorial proof of $\sum_{k=0}^n k \cdot k! = (n+1)! -1$
45219
Proving that $C$ is a subset of $f^{-1}[f(C)]$
154001
$(g\circ f)^{-1}=f^{-1}\circ g^{-1}$
100571
Prove $(1-a)(1-b)(1-c)(1-d)\geq abcd$ if $a^2+b^2+c^2+d^2=1$
156235
Are $x \cdot 0 = 0$, $x \cdot 1 = x$, and $-(-x) = x$ axioms?
76610
Show that $f^{-1}(A \cup B) = f^{-1}(A) \cup f^{-1}(B)$
59872
How to prove $\inf(S)=-\sup(-S)$?
111665
How prove this $\{a\}\cdot\{b\}\cdot\{c\}=0$ if $\lfloor na\rfloor+\lfloor nb\rfloor=\lfloor nc\rfloor$
68746
What is $f(f^{-1}(A))$?
108633
Why $f^{-1}(f(A)) \not= A$