a: =5(x^2-2xy+y^2-4z^2)
=5[(x-y)^2-4z^2]
=5(x-y-2z)(x-y+2z)
b: =(x-y)^2-z^2=(x-y-z)(x-y+z)
d: =(x-y)^2-4z^2
=(x-y-2z)(x-y+2z)
e: =3(x^2-2xy+y^2-4z^2)
=3(x-y-2z)(x-y+2z)
f: =(x-3y)^2-25z^2
=(x-3y-5z)(x-3y+5z)
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