“x^2+y^2≤1”是“|x|+|y|≤1”成立的（）A.充分不必要条件B.必要不充分条件C.充要条件D……D.既不充分也不必要条件

(x-y/1-x+y/1)÷2y/y-x计算错了，是(1/x-y-1/x+y)÷2y/y-x [(-x-y)(-x+y)-(x+y)^2-x(y-y^2)}÷1/2y 满足x-y≤1,x+y≥1,y≤3/2,则2x+y的最大值是 满足x-y≤1,x+y≥1,y≤3/2,则2x+y的最大值是 x-y≥-1,x+y≤4,y-2≥0,则2x+4y的最小值是 对于(y一撇）y`=y/x(y-1)求导,我求的结果是y``=-y^2-y`x+y/x^2(y-1)^2 怎么不对啊,我的求导过程是：y`x(y-1) - [x(y-1)]` y y`xy-y`x-(y-1+xy`)y -y^2-y`x+yy``=-------------------------=----------------------=-----------------x^2 (y-1 已知实数x,y满足条件x≥0,y≥x,3x+4y≤12,则(x+2y+3)/(x +1)的最大值是 紧急!(X-Y)^3*(X-Y)^2*(Y-X)(X-Y)^3*(X-Y)^2*(Y-X)得数是（X-Y)*(Y-X)吗?如果不是.. x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 [(1/9(x+y)^3-2(x+y)^2-2/3(x+y)]÷x+y/3x+y/3x+y是整体.. 若x+y=4,则多项式1/2(x+y)+4(x-y)-3（x-y）-3/2(x+y)-x+y值是（） 已知实数x,y满足2x-y≤2,y≤x,y≥0,则（y-1)/(x+1)的最大值是? 当x,y满足不等式组：y≤x,y≥-1,x+y≤1,目标函数t= 2x+y的最小值是? 已知x,y满足约束条件｛x+y+1≤0,x-y+1≥0,y+1≥0,则z=2x-y的最大值是? 实数x,y满足不等式组x+y≤3,x-y≥-1,y≥1,则z=4x+2y的最大值是 设x,y满足约束条件y≥0,x≥y,x+y≤1,则z=2x+y的最大值是 1、y-x/x²-y²2、(x-y)(y-z)(z-x)/(z-y)(y-x)(x-z) 化简y(x+y)+(x+y)(x-y)-x^2