(1)a²b^4-0.25c²
=(ab²+0.5c)(ab²-0.5c)
(2)(a+b)²-9
[(a+b)+3][(a+b)-3]
=(a+b+3)(a+b-3)
(3)2x²-8y²
=2(x²-4y²)
=2(x+2y)(x-2y)