,y∈R+ (23 19:53:18)1、设x,y∈R+且xy-(x+y)=1,则A.x+y≥2[(根号2)+1]B.xy≤(根号2)+1C.x+y≤[(根号2)+1] 2D.xy≥2[(根号2)+1]  

,y∈R+ (23 19:53:18)1、设x,y∈R+且xy-(x+y)=1,则A.x+y≥2[(根号2)+1]B.xy≤(根号2)+1C.x+y≤[(根号2)+1] 2D.xy≥2[(根号2)+1]   已知X,Y∈R 且1 已知A={y丨y=x²+1,x∈R,y∈R},则A=? 已知全集U={(x,y)|x∈R,y∈R},A={(x,y)|(y-3)/(x-2)=1,x∈R,y∈R},B={(x,y)|y≠x=1,x∈R,y∈R},求CuA∩CuBy≠x+1,不是y≠x=1 已知集合M={(x,y)|x-y=0,x∈R,y∈R},N={x|x+y=1,x∈R,y∈R},则集合中M∩N的元素的个数是 设集合M={(x,y)|x2+y2=1,x∈R,y∈R},N={(x,y)|x2-y=0,x∈R,y∈R},则集合M∩N是多少 设集合M={(x,y)/x2+y2=1,x∈R,y∈R},N={(x,y)/x2-y=0,x∈R,Y∈R},则集合M和N的元素交集个数为? 1.已知全集U={（x,y)|x∈R,y∈R},M={（x,y）|y-1/x+2,x∈R,y∈R},N={(x,y)|2x-y+5=0,x∈R,y∈R}.求CiM∩N=?2. |x|>1,|y|>1,x,y∈R,求证|（x-y）/（1-xy）| x,y∈R+,1/x+1/y=4,则x+2y最小值? 已知x,y∈R,求证:x+y+1≥x+y+xy 已知x,y∈R,求证:x^2+y^2≥xy+x+y-1 已知x,y,z∈R,求证:x^2+y^2>=xy+x+y-1 已知x,y∈R,求证:x-xy+y≥x+y-1 设x,y∈R,比较x^2+y^2+1与x+y+xy 已知x+2y=1,x,y∈R,求x^2y的最大值 y=x²+1,x∈R怎么解? 这两个集合为什么相等?P={y∈R|y=t2+1，t∈R}Q={t∈R|t=y2-2y+2，y∈R}这类题很让人费解啊。