x² y²=16,则x y的取值范围

1/x-1/y=(y-x)/xy=-3y=x=-3xyx-y=3xy所以原式=[5(x-y)+xy]/(x-y)-xy]=[5(3xy)+xy]/[(3xy)-xy]=16xy/2xy=8

x-xy=8(1)xy-y=-9(2)则有(1)-(2):X-XY-XY+Y=X+Y-2XY=8-(-9)=17

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x的平方-xy=16.(1)xy-y的平方=-8.(2)(1)*4-(2)*3,得(4x的平方-4xy)-(3xy-3y的平方)=16*4-(-8)*34x的平方-7xy+3y的平方=64+24=88

(3x-4y+5xy)-(2x-3y)+5xy=3x-2x-4y+3y+5xy+5xy=x-y+10xy=3+4×10=43

（3x-4y+5xy）-（2x-3y）+5xy=3x-4y+5xy-2x+3y+5xy=(x-y)+10xy=3+50=53

x^+2xy+y^+4=16(x+y)²=16-4=12(1)x^-2xy+y^=16(x-y)²=16(2)(1)-(2)2y*2x=-4xy=-1(3xy+6y^)+|x^-(

原式=-x^3y^6+x^2y^4+xy^2=27+9+xy^2

已知2x-3*根号(xy)-2y=0(x>0),则x2+4xy-16y2除以2x2+xy-9y2的值是多少?2x-3*根号(xy)-2y=0(根号X-2根号Y)(2根号X+根号Y)=0根号X-2根号Y

1/x-1/y=3(y-x)/xy=3y-x=3xyx-y=-3xy(5x+xy-5y)/(x-xy-y)=[5(x-y)+xy][(x-y)-xy]=(-15xy+xy)/(-3xy-xy)=-14

解题思路：将原方程右边分解因式为（x-4y)(x+y)=0,可得x=4y或x=-y,进而可求出x与y的比值。解题过程：解：∵x2-3xy-4y2=0∴（x-4y)(x+y)=0∴x=4y或x=-y∵x

两式相加,得（x²+2xy+y²）+（x+y）-42=0即（x+y）²+（x+y）-42=0所以[(x+y)+7][(x+y)-6]=0所以x+y=-7或x+y=6

1/x+1/y=-2则(x-xy+y)/(x+xy+y)分子分母同除以xy=(1/x+1/y-1)/(1/x+1/y+1)=(-2-1)/(-2+1)=3

2x-3*根号(xy)-2y=0(根号X-2根号Y)(2根号X+根号Y)=0根号X-2根号Y=0时X=4Y2根号X+根号Y=0时X=Y=0(不合题意,舍去)x2+4xy-16y2除以2x2+xy-9y

原式=xy-2y+3x+5y=xy+3x+3y=xy+3(x+y)=-1+3×2=5

(3x-4y+5xy)-(2x-3y-2xy)=3x-4y+5xy-2x+3y+2xy=x-y+7xy=4+7×(-2)=4-14=-10

解题思路：：∵x+y=0,x+13y=1，解得x=1/12,y=-1/12∴x²+12xy+13y²=1/144-1/12+13/144=14/144-1/12=2/144=1/72解题过程：已知x+

∵x-y=4xy，∴2x+3xy-2yx-2xy-y=2(x-y)+3xyx-y-2xy=8xy+3xy4xy-2xy=112．故答案为：112．

由x,y为正得x=y/(y-1)>0、y=x/(x-1)>0,所以x>1、y>1,因此x+2y=y/(y-1)+2y=（y-1+1)/(y-1)+2(y-1+1)=3+1/(y-1)+2(y-1)>=

由式1通分得(y-x)/xy=-3y-x=-3xy代入式2得原式=4xy/2xy=2