Ответ:

  1. \(ax+bx+ac+bc=x(a+b)+c(a+b)=(a+b)(x+c)\);
  2. \(3a-3c+xa-xc=3(a-c)+x(a-c)=(a-c)(x+3)\);
  3. \(4a+by+ay+4b=a(4+y)+b(y+4)=(a+b)(y+4)\);
  4. \(6x+7y+42+xy=6x+42+y(x+7)=6(x+7)+y(x+7)=(x+7)(y+6)\);
  5. \(px+py-5x-5y=p(x+y)-5(x+y)=(x+y)(p-5)\);
  6. \(ab-ac-4b+4c=a(b-c)-4(b-c)=(a-4)(b-c)\).