x+y=80 5x+2.5y≤290 1.5x+3.5y≤212
x+y=5; x^y+y^x=17
x=3,y=-x+5(x>1) y=-x+5(x≤1),y=?
已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y)
{(x,y) |x|+|y|
x>y?x:y
已知集合A={(x,y)|x²+y²≤1.x.y∈R},B={(x,y)||x|+|y|≤2.x.y
设变量x y满足约束条件x-y≥-1 x+y≥1 2x-y≤1 z=(x-2y)/(x+y)的最大值
先化简再求值(x-y)(x+y)-(x-2y) 的完全平方+x(3x-5y)-(x-y)(x-2y),其中x=1/2 y
x+y=6 10x+y≤42
Y={X (-5
y=-3x,-2≤x
(5x+3y)(3y-5x)-(4x-y)(4y+x)=