If $x$ and $y$ are not both $0$ then $ x^2 +xy +y^2> 0$
27911
How can I prove that $xy\leq x^2+y^2$?
154327
$A^2X = X$ show that $AX = X$, if $A_{ij} > 0$ and $x_{i} > 0$
36507
If $x,y>0$ and $x^2+y^3\ge x^3+y^4$, prove that $x^3+y^3 \le 2$.
79040
Graph of $|x| + |y| = 1$
73073
Differentiating $y=x^{2}$
1102
Way to determine if X and Y are both over 0
29540
Method to eliminate $x$ between the equation $x^2 + ax + b = 0$ and $xy+ l(x + y) + m = 0$
72920
$x \perp y$ if and only if $\Vert x + \alpha y \Vert \ge \Vert x \Vert$ for all scalars $\alpha$
45555
$(x+y)^c\le x^c+y^c$ for $0<c\le1$
96554
Why is $x^0 = 1$ except when $x = 0$?
96153
$ x^3<y^3 \iff x<y $ proof issue.
77464
Prove that ${x dy - y d x\over x^2 + y^2}$ is not exact
47809
If $x,y\in\mathbb Z$, solve $x^2+xy+y^2=x^2y^2$.
155757
Number theory: $x^y + 1 = y^x$
10068
$f(x,y)= e^{-\frac{1}{x^2+y^2}}$ when $(x,y)\neq (0,0)$ and $f(0,0)=0$.
28822
$|x| - |y| \leq |x-y|?$
86211
If $x+y+z \geq xyz$ Prove that $x^2 + y^2 + z^2 \geq xyz$.