先化简,再求值:2x2+(-x2-2xy+2y2)-3(x2-xy+2y2),其中x=2,y=-12
先化简,再求值:2x2+(-x2-2xy+2y2)-3(x2-xy+2y2),其中x=2,y=-12
先化简再求值:-(x2+y2)+[-3xy-(x2-y2)],其中x=-1,y=2.
先化简再求值2(x2-xy)-3(2x2-3xy)-2[x2-(2x2-xy+y2)],其中x=-1,y=-2.
先化简,再求值:(-3xy)2(x2+xy-y2)-3x2y2(3x2+3xy+y2),其中x=-43
先化简,再求值:(1)2x2-5x x2 4x,其中x=-3 (2)(3x2-xy-2y2)-2(x2 xy-2y2),
先化简,后求值:4xy-(2x2+5xy-y2)+2(x2+3xy),其中|x+2|+(y−12)
已知2x=3y,求xy/(x2+y2)-y2/(x2-y2)的值
x(x-1)-(x2-y)=-3,求x2+y2-2xy的值
若x<y<0,则x2−2xy+y2+x2+2xy+y2=( )
已知X2-2x+y2+6y+10=0,求(x2-2xy)/(xy+y2)的值
已知:x=3,y=-5,x2-2xy+y2/x2-y2的值是
已知x2+y2=20,x2+xy-2y2=2(x+2y),求x+y的值