Question

下列变形中正确的有( )①x2-y2x-y=(x2-y2)(x+y)(x-y)(...

下列变形中正确的有( ) ①x2-y2x-y=(x2-y2)(x+y)(x-y)(x+y)=(x2-y2)(x+y)x2-y2=x+y; ②ab2-a2b3=ab2÷ab-a2b3÷ab=-bab2; ③n2m=np2mp; ④m4-81m2-9=(m2+9)(m2-9)m2-9=m2+9.A.1个B.2个C.3个D.4个

Answer 1

解答:解:①当x+y=0时，
x2-y2
x-y
≠
(x2-y2)(x+y)
(x-y)(x+y)
，应该是:
x2-y2
x-y
=
(x+y)(x-y)
x-y
=x+y，故本小题猛芦错误;
②结果不是最简分式，应该是:
ab2
-a2b3
=
ab2÷ab2
-a2b3÷ab2
=-
1
ab
，故本小题错误;
③纳知明当p=0时，
n
2m
≠
np
2mp
，故本洞告小题错误;
④正确.
故选A.