Answer:
-2
Step-by-step explanation:
5+14a=9a-5
+5 +5
10+14a=9a
-9a -9a
10+5a=0
-5a -5a
10= -5a
÷5 ÷5
2= -a
*-1 *-1
-2=a
This is a geometric sequence with first term 1 and common ratio -1/2. r=-1/2.
a(n) = a(1)*(r)^(n-1).
Check: If n=2 our formula must return -1/2. Does it?
a(2) = 1(-1/2)^(2-1) = (-1/2)^1 = - 1/2. Yes.
a(3) should be 1/4. Is it? a(3) = (-1/2)^(3-1) = 1/4 Yes.
Then a(8) = (-1/2)^(8-1) = (-1/2)^7 = -1 / 2^7 = -1/128 (answer)
