Answer:
The value of a7 is 128
Step-by-step explanation:
* Lets revise the rule of the geometric series
-There is a constant ratio between each two consecutive numbers
- Ex:
# 5 , 10 , 20 , 40 , 80 , ………………………. (×2)
# 5000 , 1000 , 200 , 40 , …………………………(÷5)
* General term (nth term) of a Geometric series:
# a1 = a , a2 = ar , a3 = ar2 , a4 = ar3 , a5 = ar4
# an = ar^n-1, where a is the first term , r is the constant ratio
between each two consecutive terms
, and n is the position
of the term in the series
* Now lets solve the problem
∵ a = 2
∵ r = -2
* To find a7 put n = 7
∵ an = a (r)^n - 1
∴ a7 = 2 (-2)^(7 - 1) = 2 (-2)^6
∵ (-2)^6 = 64 ⇒ even power canceled the negative sign
∴ a7 = 2 (64) = 128
∴ The series is : 2 , -4 , 8 , -16 , 32 , -64 , 128 , ............
* The value of a7 is 128
