Chapter 11 - 11.3 - Geometric Sequences and Series - 11.3 Exercises - Page 795: 13

$a_1=4$ $a_2=-12$ $a_3=36$ $a_4=-108$ $a_5=324$

$a_n=a_1r^{n-1}$ $a_1=4,~~r=-3$ $a_2=4(-3)^{2-1}=4(-3)^1=4(-3)=-12$ $a_3=4(-3)^{3-1}=4(-3)^2=4(9)=36$ $a_4=4(-3)^{4-1}=4(-3)^3=4(-27)=-108$ $a_5=4(-3)^{5-1}=4(-3)^4=4(81)=324$