A) 3a^3-75ab^2=3a(a^2-25b^2)=3a(a^2-5b^2)=3a(a-5b)(a+5b)
б) x-y-x^2+2xy-y^2=(x-y)-(x^2-2xy+y^2)=(x-y)(x-y^2)=(x-y)(1-(x-y))=(x-y)(1-x+y)
в) (2-x)(2+x)-a (a-2x)=2^2-x^2-a(a-2x)=2^2-x^2-a^2+2ax=2^2-(x^2-2xa+a^2)=2^2-(x-a)^2=(2-(x-a))(2+(x-a))=(2-x+a)(2+x-a)