Question

下列恒等变形中，属于因式分解的个数有
①a²-b²＝(a+b)(a-b)
②(a-1)²＝a²-2a+1
③x²-y²-1＝(x+y)(x-y)-1
④(x-y)²+(y-x)³＝(x-y)²(1-x+y)

1. A.
   1个
2. B.
   2个
3. C.
   3个
4. D.
   4个

Answer 1

B