Question

化简或求值（1）[2aa2−4+1/2−a]；（2）(xx−y−2yx−y)•xyx−2y÷(1x+1y)；（3）x3−

Answer 1

（1）原式=[2a

(a+2)(a−2)-

1/a−2]

=[2a

(a+2)(a−2)-

a+2

(a+2)(a−2)

=

a−2

(a+2)(a−2)

=

1/a+2]；

（2）原式=[x−2y/x−y]•[xy/x−2y]÷[x+y/xy]

=[x−2y/x−y]•[xy/x−2y]•[xy/x+y]

=

x2y2

x2−y2；

（3）

x3−x2

x2−x-

1−x2

x+1

=

x2(x−1)

x(x−1)-

(x+1)(1−x)

x+1

=x-（1-x）

=2x-1，

当x=2时，原式=3．