[tex]\text{If}\ a_1;\ a_2;\ a_3;\ ...;\ a_n\ \text{is a geometric sequence, then}\ \dfrac{a_n}{a_{n-1}}=const.[/tex]
[tex]A.\\1;\ 5;\ 9;\ 13;\ ...\\\\\dfrac{5}{1}=5\\\dfrac{9}{5}\neq5\\\\B.\\\dfrac{1}{4};\ \dfrac{1}{2};\ 1;\ 2;\ 4;\ ...\\\\\dfrac{\frac{1}{2}}{\frac{1}{4}}=\dfrac{1}{2}\cdot\dfrac{4}{1}=2\\\dfrac{1}{\frac{1}{2}}=1\cdot\dfrac{2}{1}=2\\\dfrac{2}{1}=2\\\dfrac{4}{2}=2\\\text{the geometric sequence}[/tex]
[tex]C.\\2;\ 3;\ 5;\ 9;\ 17;\ ...\\\\\dfrac{3}{2}=1.5\\\dfrac{5}{3}\neq1.5\\\\D.\\3;\ -15;\ -33;\ -51;\ -69;\ ...\\\\\dfrac{-15}{3}=-5\\\dfraxc{-33}{-15}=\dfrac{11}{5}\neq-5\\\\\boxed{\text{Answer is B.}} [/tex]
