( )-(x2+3xy)=-xy-1/3y2括号里添几

( )-(x2+3xy)=-xy-1/3y2括号里添几 5x2*3xy= 解方程组 x2 -2xy -y2 =1 2x2 -5xy -3y2 =0 已知x2+xy=3,xy+y2=-2,则2x2-xy-3y2= 已知x2-3xy=-5,xy+y2=3,求x2-2xy+y2. 若X2+xy-2y2=0,则（x2+3xy+y2)/x2+y2=? -(x2+y2)+[-3xy-(x2-y2)]化简X=-1,y=2X2表示X的2次方 3XY表示XY乘3 2(x2-xy)-3(2x2-3xy)-2[x2-(2x2-xy+y2)] 化简. (3xy-9x2-2y2-6xy)-(6x2+2xy-3xy-y) x2-3y2=2xy过程 x2—2xy=3y2 2xy+y2=1 怎么解这个方程组? 先化简,再求值：5x2-[2xy-3（xy+2）+4x2] ,其中x=-2,y= .先化简,再求值：5x2-[2xy-3（xy+2）+4x2] ,其中x=-2,y=1/2 . 解方程组 x2 -2xy -y2 =1 2x2 -5xy -3y2 =0解方程组 x2 -2xy -y2 =12x2 -5xy -3y2 =0 因式分解x2+xy-3y2 X2+3xy+y2因式分解 怎么解二元二次方程.例如 X2+xy+y=1 ,X2+xy+x-3=3 怎么解 4xy+6xy-3xy=? 2xy-xy-(-3xy)=