For the following exercises, use the Rational Zero Theorem to help you solve the polynomial equation.
25. 2 x^{3}-3 x^{2}-18 x-8=0
26. 3 x^{3}+11 x^{2}+8 x-4=0
27. 2 x^{4}-17 x^{3}+46 x^{2}-43 x+12=0
28. 4 x^{4}+8 x^{3}+19 x^{2}+32 x+12=0
For the following exercises, use Descartes' Rule of Signs to find the possible number of positive and negative solutions.
29. x^{3}-3 x^{2}-2 x+4=0
30. 2 x^{4}-x^{3}+4 x^{2}-5 x+1=0