有一道题先化简再求值(x+2y)(x-2y)-x(x-y)-xy其,中x=根号2,y=-根号3,小明做题时把x=根号2,

有一道题先化简再求值(x+2y)(x-2y)-x(x-y)-xy其,中x=根号2,y=-根号3,小明做题时把x=根号2, 代数式求值.已知x=2,y=根号3,求 (根号x-根号y)/(根号x+根号y)+(根号x+根号y)/(根号x-根号y) {（x-y)/(根号x+根号y)}-(x+y-2倍根号xy)/(根号x-根号y)=? 化简求值:根号x^-2xy+y^2 + x^2 -6xy+9y^2/x-3y,其中x=根号3,y=根号5 已知y=根号1-x+根号x-1+3,求根号x+根号y分之x+2根号xy+y+根号x-根号y分之一的值 已知y=根号(x-8)+根号(8-x)+18,求代数式[(x+y)/(根号x+根号y)]-2xy/(x根号y-y根号x) x根号x+x根号y/xy-y^2)-（x+根号xy+y/x根号x-y根号）y (x+y)/(根号下x+根号下y)+2xy/(x根号下y+y根号下x)=______. 化简,求值：(1/x+y)+(1/x-y)除以(2x/x^2-2xy+y^2)其中x=根号3,y=负根号2 化简:((根号x-根号y)^3+2x根号x+y根号y)/(x根号x+y根号y)+(3根号xy-3y)/(x-y) 先化简再求值（x-y/1-x+y/1）÷x平方+2xy+y平方/2y,其中x=根号3+2,y=根号3 先化简再求值：xy^3÷(-xy)+(x+2y)(x-2y),其中x=根号2,y=1