证明：若x+y>6,xy>9,则x>3,y>3是假命题举一个例子

证明：若x+y>6,xy>9,则x>3,y>3是假命题举一个例子 若M=3x^2-8xy+9y^2-4x+6y+13,证明：M>0 证明|xy|=|x||y| 证明|xy|=|x||y| 已知x-y=3xy,且xy不等于0,则-3x+6xy+3y/(7x-5y)-9xy-(3x-y) (x-2xy)*(-xy+2y*y)-(3x*x-2xy)(x-9xy+6y*y)答案应为-2x-x*x-3x， 若xy/(x+y)=3,则(6x+4xy+6y)/(9x+4xy+9y)=______ 化简：x-y/x+3y÷x^-y^2/x^2+6xy+9y^2-(xy/x+y) 证明:(y/x)+(x/y)+xy≥x+y+1 若x+y分之xy=2,则-x+3xy-y分之3x-xy+3y=多少? 若xy/x+y=2,则3x-5xy+3y/-x+3xy-y=?/是分之 若x+y分之xy=2,则-x+3xy-y分之3x-xy+3y=多少? 若xy/x+y=2,则3x-xy+3y/-x+3xy-y= 证明:无论x、y为何值时,M=3x^2-8xy+9y^2-4x+6y+13恒为非负数 若x-y=4,xy=1,则(2x+y-2xy)-(3x+2y+xy)-(4xy+3y-5x)= (9x^2y-6xy^2)/3xy 若2x^2-6xy+9y^2-4x+4=0,则y/x-x/y=若2x^2-6xy+9y^2-4x+4=0,则y/x-x/y=? 若3|x-3|+x^2-6xy+9y^2=0 则x^2y^2+2xy=________