(1)原式=
x2−y2
y−x
=
(x+y)(x−y)
y−x
=-(x+y);
(2)原式=
3x(x+1)−x(x−1)
(x+1)(x−1)•
(x+1)(x−1)
x
=
x(x2+4)
(x+1)(x−1)•
(x+1)(x−1)
x
=2x+4,
当x=2时,原式=4+4=8.
(1)原式=
x2−y2
y−x
=
(x+y)(x−y)
y−x
=-(x+y);
(2)原式=
3x(x+1)−x(x−1)
(x+1)(x−1)•
(x+1)(x−1)
x
=
x(x2+4)
(x+1)(x−1)•
(x+1)(x−1)
x
=2x+4,
当x=2时,原式=4+4=8.