先化简(x2-2x+1-y2)/(x+y-1),并求当x-y=12时,该式的值．

先化简,再求值:2x2-y2+2y2-3x2-2y2+x,其中x=-1,y=2 3y2-x2+(2x-y)-2(x2+3y2),其中x=1,y=-2先化简,再求值. y=x+√(1-x2) y2=x2+(1-x2)+2x√(1-x2) 已知x,y满足（x2+y2）(x2+y2-1)=2,则x2+y2的值为多少?x2,y2表示x和y的平方 思考题：先化简,再求值：(xy-y2)÷x2-2xy+y2/y×x2-y2/y2,其中x=1/2,y=-1 x2+x+y2/x+y 已知实数x.y满足（x2+y2）（x2+y2-1）=2,求x2+y2的值 [2/xy/(1/x+1/y)2+(x2+y2)/(x2+2xy+y2)]*2x/(x-y) x2-2x+2y-y2因式分解 因式分解x2+y2-xy-x-y+1 (x2-4y2)-(x+2y)因式分解 因式分解(x2-y2)-(x-y)2快 2/1(x2-y)+3/1(x-y2)+6/1(x2+y2) x-y=1 证明x2+y2+1/x2+1/y2大于等于17/2 x2+y2=1和x2+y2-4x+2y=4解这组方程, 1.x2+(1+x)2+(x+x2)22.(x+y)4+(x2-y2)2+(x-y)4 1.(x-y)(x2+xy+y2) 2.求值x2(x-1)-x(x2+x-1),其中x=2分之一 x2-2xy+y2-1/x-y-1