What is the sum of the geometric sequence −3, 18, −108, … if there are 8 terms? 719,835 119,973 −119,973 −719,835

Sn = a1 (1-r^n) / (1-r)

= -3 (1- (-6)^7) / (1-(-6))

= -3 (1-(-279936)) / 7

= -3 (279937) / 7

= -119,973 #

Step-by-step explanation:

i belive those are the ones that are under 90 degreese.

a 4/6 = 9/12   not proportional

step-by-step explanation:

to find which are not proportional, we can use cross products

if it is true, they are proportional.   if it is not true, they are not proportional.

a 4/6 = 9/12

4* 12 = 6*9

48 = 54

not this is not proportional  

b 2/3 = 12/18  

2* 18 = 3 * 12

36 = 36

this is proportional

c 5/4 = 10/8  

5*8 = 4*10

40 = 40

this is proportional

d 7/5 = 35/25

7*25 = 5 * 35

175 = 175

is proportional