已知x+y=-5,xy=3,则xx+yy=( ) A.25 B.-25 C.19 D.-19

已知2x=3y,求xy/xx+yy-yy/xx-yy的值 已知x（x+1)-(xx+y)=3,求(xx+yy)/2-xy的值 已知(x+y)(x+y)=25,(x-y)(x-y)=9求xy与xx+yy的值 已知x=1/2 y=1/3 z=1/4 则(xx+yy-zz+2xy)/(xx-yy+zz-2xz) 得多少? 已知xx+xy=1,xy-yy=-4,则xx+2xy-yy= 已知x,y是实数,且适合方程(xx+xy-12)(xx+xy-12)+(xy-2yy-1)(xy-2yy-1)=0求x, x(x+1)-(xx+y)=-3,求(xx+yy)/2-xy的值 已知：xx-xy=7,xy-yy=4,则xx-yy=( ） 知x/3=y/4=z/5,求(xy+yz+xz)/xx+yy+zz 已知xx+yy+4x-6y+13=0,求（xx-2x）/xx+3yy的值. 已知x-y=5,y-z=4,求xx+yy+zz-xy-yz-xz的值 设集合A=｛x-y,x+y,xy},b={xx+yy,xx-yy,0},且A=B,求实数x与y的值及集合AB