15x^2-47xy+28y^2

（xy-x^2)乘以(xy)/(x-y) 如果x^2+xy+y-14,y^@+xy+x=28,求x+y的值. （x^2+xy/x-y)/（xy/x-y)计算 2x^2-xy-15y^2 6x^2y^2+xy-15 (x+y-2xy)(x+y-2)+(1-xy)² (x^2-xy)y÷y-x/xy怎么做? (x-2xy)*(-xy+2y*y)-(3x*x-2xy)(x-9xy+6y*y) x-y/x²÷x²-2xy+y²/xy*（xy-x²） 作乘法:(x+y)(x^2-xy+y^2)；(x-y)(x^2+xy+y^2) x^2-xy-6y^2+3xy+y+2 计算（xy-y^2)÷x-y/xy