x+y=9 xy=16 x^2+y^2=?

已知x^2+xy=16 y^2+xy=9 求(x+y) (x-y)分别是 x+y x-y 不是乘 已知x-xy=8,xy-y=-9,求x+y-2xy的值 |x|/x+y/|y|+xy/|xy|= f(xy,x-y)=x^2+y^2+xy;f(x,y)/∂x;f(x,y)/∂y x*x+xy=3,xy+y*y=2,则x*x+2xy+y*y=________? x^+2xy+y^+4=16 x^-2xy+y^=16 求(3xy+6y^)+|x^-(2xy+2y^-3x^)|的值 已知2x-3根号xy-2y=0(x>0),求x^2+4xy-16y^2/x^2+xy-9y^2 已知x*x-4xy+4y*y=0 求[2x(x+y)-y(x+y)]/(4x*x-4xy+y*y)的值? x+y=-3 xy+x+y=-2 x/y+y/x=? (-x+2y)(2x+y)-(2x+y)(y-2x)-3xy=?因式分解 f(x+y,x-y)=(x^2-y^2)/2xy,求f(x,y)! 正数x,y满足x-y=2xy,求x-y/x+y的值. f(x+y,x-y)=2xy(x-y),求f(x,y) x^2+xy+x=36,y^2+xy+y=20,求x+y. 若x^2+xy+y=14,y^2+xy+x=28,求x+y 函数f(xy,x+y)=x^2+xy+y^2,则df(x,y)=? f(xy,x-y)=x^2+3xy+y^2,则f(x,y)=? 如果x^2+xy+y-14,y^@+xy+x=28,求x+y的值.