2a平方-4a
=2a(a-2)
4x平方-25
=(2x-5)(2x+5)
4a平方-1
=(2a-1)(2a+1)
9x平方-y平方-4y-4
=9x²-(y²+4y+4)
=9x²-(y+2)²
=(3x-y-2)(3x+y+2)
2a平方-4ab+2b²
=2(a²-2ab+b²)
=2(a-b)²