1. 5x 4 – 405 = 5(x 4 – 81) = 5(x 2 + 9)(x 2 – 9) = 5(x 2 + 9)(x + 3)(x – 3) by D. Fisher

3. x 2 + 10x + 16 = (x + 8)(x + 2)

4. x 2 + 4x – 21 = (x + 7)(x – 3)

5. 2x 2 + 7x + 3 = (2x + 1)(x + 3)

7. 3x 2 y + 12xy = 3xy(x + 4)

8. x 3 + 5x 2 – x = x(x 2 + 5x – 1)

10. x 2 – 81 = (x + 9)(x – 9)

11. 4x 2 – 121 = (2x + 11)(2x – 11)

13. x 2 – 14x + 49 = (x – 7) 2

14. x 2 + 8x + 16 = (x + 4) 2

15. 25x 2 – 10x + 1 = (5x – 1) 2

17. x 2 – x – 6 = (x – 3)(x + 2)

18. 3x 2 +24x + 21 = 3(x + 1)(x + 7) = 3(x 2 + 8x + 7)

19. x 4 – 16 (x 2 + 4)(x – 2)(x + 2) = (x 2 + 4)(x 2 – 4)

20. x 2 y +4xy + 4y = y(x + 2) 2

21. 9x 2 + 6x + 1 = (3x + 1) 2

22. 2x 2 – 18x + 40 = 2(x – 4)(x – 5)