Chapter 9 - Conic Sections, Sequences, and Series - 9.4 Geometric Sequences - 9.4 Exercises - Page 736: 9

Geometric with ratio $r=-3$

$4, -12, 36, -108, 324, -972, . . . $ $\frac{a_2}{a_1}=\frac{-12}{4}=-3=r$ $ra_2=-3\times(-12)=36=a_3$ $ra_3=-3\times(36)=-108=a_4$ $ra_4=-3\times(-108)=324=a_5$ and so on. The sequence is geometric with common ratio $r=-3$.