Question

Which sequence is geometric

Answer 1

If a, b, c, d is geometric sequence, then

$\dfrac{b}{a}=\dfrac{c}{b}=\dfrac{d}{c}=const.$

A. 5; 15; 25; 35

$\dfrac{15}{5}=3;\ \dfrac{25}{15}=\dfrac{5}{3}-NOT$

B. 5; 10; 20; 40

$\dfrac{10}{5}=2;\ \dfrac{20}{10}=2;\ \dfrac{40}{20}=2-YES$

C. 6; 12; 18; 24

$\dfrac{12}{6}=2;\ \dfrac{18}{12}=\dfrac{3}{2}-NOT$

D. 7; 14; 21; 28

$\dfrac{14}{7}=2;\ \dfrac{21}{14}=\dfrac{3}{2}-NOT$

Answer: The sequence B. 5; 10; 20; 40 is geometric.