Help with factorization?!

please i need help on solving this problems, of factorization:
1)3x^6-3x^5-12x^5+12x^4
2)5x^4y^2+20x^3y^2-15x^3y^2-60x^2y^2
3)x^4-x^2y^2
4)x^7y^2-x^4y^2
5)x^5-16x

Hello,

3x⁶ - 3x⁵ - 12x⁵ + 12x⁴
  = 3x⁴(x² - x - 4x + 4)
  = 3x⁴[x(x - 1) - 4(x - 1)]
  = 3x⁴(x - 1)(x - 4)

5x⁴y² + 20x³y² - 15x³y² - 60x²y²
  = 5x²y²(x² + 4x - 3x - 12)
  = 5x²y²[x(x + 4) - 3(x + 4)]
  = 5x²y²(x + 4)(x - 3)

x⁴ - x²y²
  = x²(x² - y²)
  = x²(x - y)(x + y)

x⁷y² - x⁴y²
  = x⁴y²(x³ - 1)
  = x⁴y²(x - 1)(x² + x + 1)

x⁵ - 16x
  = x(x⁴ - 16)
  = x(x² + 4)(x² - 4)
  = x(x² + 4)(x + 2)(x - 2)

Regards,
Dragon.Jade :-)