PLEASE HELP!!!!!!!! What is the 8th term of this sequence? 1,-1/2,1/4,-1/8

1 answer:

7 0

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)

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