解
18a²-50
=2(9a²-25)
=2(3a-5)(3a+5)
2x²y-8xy+8y
=2y(x²-4x+4)
=2y(x-2)²
a²(x-y)-b²(x-y)
=(a²-b²)(x-y)
=(a-b)(a+b)(x-y)
a的4次方-16
=(a²-4)(a²+4)
=(a-2)(a+2)(a²+4）