若X+Y=6,X^2-Y^2=42,则X-Y=?

若(x-y)/(x+y)=3 则(x+2y)/(6x-7y)等于 设x>1,y>0,若x^y+x^-y=2根号2,则x^y-x^-y等于 【2(x-y)^3-8(x-y)^2(x+y)+6y(x-y)^2】/2(x-y)^2= 若5x+3y=3x+4y=x+2y+6,则x+y=___ [x(x-y)-y(x-y)+(x+y)(x-y)]÷2x其中x=2012 y=2013 6(x-y)-2(x+y)=14 3(x-y)+(x+y)=5 x+y/2+x-y/3=6,4(x+y)-3(x-y)=-20 {(x+y)/2+(x-y)/3=6 4(x+y)-3(x-y)=-20 4(x+y)-3(x-y)=-20,2/x+y+3/x-y=6 {3(x+y)-4(x-y)=4 {x+y/2 + x-y/6=1 若3x-5y=0,则x+y/x=（）,x-y/y=（）,2x-3y/2x+3y=( ) 若全集I={(x,y)|x,y∈R},集合M={(x,y)|(y-3)/(x-2)},N{(x,y)|y=x=1},则(