先化简,再求值:2x2+(-x2-2xy+2y2)-2(x2-xy+2y2),其中x=-1,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:(1)2x2-5x x2 4x,其中x=-3 (2)(3x2-xy-2y2)-2(x2 xy-2y2),
先化简,再求值:(-3xy)2(x2+xy-y2)-3x2y2(3x2+3xy+y2),其中x=-43
先化简,后求值:4xy-(2x2+5xy-y2)+2(x2+3xy),其中|x+2|+(y−12)
x(x-1)-(x2-y)=-3,求x2+y2-2xy的值
已知2x=3y,求xy/(x2+y2)-y2/(x2-y2)的值
已知x-y+1,X2+Y2=25 求(x+y)2和x2-xy+y2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x2+4y2+x2y2-6xy+1=0,求 x4-y4/2x-y 乘 2xy-y2/xy-y2 除以(x2+y2/x