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1) 7x^2-28 = 7(x^2-4) = 7(x-4)(x+4);

2) 3a^3-108a = 3a(a^2-36) = 3a(a-6)(a+6);

3) 3x^4-3x^2y^2 = 3x^2(x^2-y^2) = 3x^2(x-y)(x+y);

4) 4m^4n^2-64m^4p^2 = 4m^4(n^2-16p^2) = 4m^4(n-4p)(n+4p);

5) 3x^2 - 48xy+192y^2 = 3(x^2-16xy+64y^2) = 3(x-8y)^2