Chapter 9 - Conic Sections, Sequences, and Series - 9.4 Geometric Sequences - 9.4 Exercises - Page 736: 10

Geometric with ratio $r=-2$

$ 8, -16, 32, -64, 128, -256, . . .$ $\frac{a_2}{a_1}=\frac{-16}{8}=-2=r$ $ra_2=-2\times(-16)=32=a_3$ $ra_3=-2\times(32)=-64=a_4$ $ra_4=-2\times(-64)=128=a_5$ and so on. The sequence is geometric with common ratio $r=-2$.