Question

The question is in the image. I really need help, please.

Answer 1

Answer:

  (b)  65/27

Step-by-step explanation:

Here, we notice the index for the summation runs from 0 to 3, so there are a total of 4 terms.

The sum represented by the summation symbol is ...

  5(-2/3)^0 +5(-2/3)^1 +5(-2/3)^2 +5(-2/3)^3

  = 5(1 -2/3 +4/9 -8/27)

  = 5/27(27 -18 +12 -8)

  = 5(13/27) = 65/27

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There is a formula for the sum of a geometric series:

  Sn = a1×(1 -r^n)/(1 -r)

Here, the first term is a1 = 5(-2/3)^0 = 5. The common ratio is the base of the exponential, r = -2/3. So, the sum of n=4 terms is ...

  S4 = 5×(1 -(-2/3)^4)/(1 -(-2/3)) = 5×(1 -16/81)/(5/3) = 65/27