12. Explain why each expression is or is not a perfect square trinomial. (1) x + 6x + 12 (2) x +18x + 81

(3) x + 15x + 25

15. Explain why you must multiply the numerator and denominator of a complex number by the denominator's complex conjugate when dividing complex numbers.

17. A certain quadratic function has the factors (2x - 5) and (3x + 4). What are the zeros of the function?

x = and x = 4/3

x = 5/2 and x = -4/3

x = 5 and x = -4

x = -2 and x = -3

18. Describe how you can use the factors of a quadratic function to find its zeros. Be specific.