GRE
z
0
$$(x-y)^{2}$$
$$x^{2}+y^{2}$$
$$(a+\frac{1}{a})^{2}$$
2
x
10
x+2y
y+2x
y
The average of x and z
x-y
$$\frac{n}{x}$$
n
$$\frac{x}{x+1}$$
1
25000 +道题目
236本备考书籍