若xy=2,求1/(4x^2)+1/(9y^2)的最值

1-2/x+y=xy,4y+6x=xy.求xy的解? 若x-y=4,xy=1,求(-2xy+2x+3y)-(3xy+2y-2x)-(x+4y+xy)的值 若x-y=4,xy=-1求(-2xy+3x+4y）-（3xy+9y-2x)的值 已知x y=1,xy=-3,求2xy-4x 4(y-2(xy-x)) 若1/x-1/y=2,求3x-2xy-3y/x-xy-y的值3x-2xy-3y/x-xy-y 不好意思，是3x-2xy-3y/x-2xy-y 若（x+1)^2+|y-2|=0,求3x^2-[5xy-(x^2y-3xy)+4x^2y-8xy]的值 数学题x²-xy=4 y²-xy=9x²-xy=4 y²-xy=9 求：（1）x²-2xy+y²（2）x²-y² 已知X+Y=3,XY=-1,求2(X-Y)^4-9(X-Y)^2+12XY 已知1/x-1/y=2,求3x+7xy-3y/2x-3xy-2y答案是1/x-1/y=2(y-x)/xy=2 得：x-y=-2xy(3x+7xy-3y)/(2x-3xy-2y)=[3(x-y)+7xy]/[2(x-y)-3xy]=(-6xy+7xy)/(-4xy-3xy)=xy/(-7xy)=-1/7 谁能帮我解释一下=[3(x-y)+7xy]/[2(x-y)-3xy]=(-6xy+7xy)/(-4xy-3xy) 是怎 若1/X-1/Y=3,求5X+2XY-5Y/X-4XY-Y 若1/x-1/y=3,求5x+2xy-5y/x-4xy-y的值 若(1/x )-(1/y)=3,求(3x+4xy-3y)/(x-2xy-y)的值. x-y=1,xy=2.求：(-2xy+2x+3y)-(3xy+2y-2x)-(x+4y+xy)的值 .已知:x-y=1,xy=-2.求:(-2xy+2 x+3y)-(3xy+2y-2x)-(x+4y+xy)的值 1若x+2y=0 ,xy不等于0,求分式 x^2+2xy / xy+y^2 若xy满足x²+2x+y-2√y-1=-1,求xy, 若x,y满足x^+2y^-2xy+1=0,求xy的值 若(1)xy>0,(2)xy<0,求|x|/x+|y|+|xy|/xy的值