Math, asked by 1giffenkat, 10 months ago

determine the sum of the geometric series 7-14+28-...-3584

Answers

Answered by k047
2

Here your ans

S = 7 + 14 + 28 + ... + 3584

2 S = 2 (7 + 14 + 28 + ...1792 + 3584) =

2*7 + 2*14 + +...+ 2* 1792 + 2*3584 =

14 + 28 + ...+ 3584 + 7168 =

S - 7 + 7168 = S + 7161

2S = S + 7161 --------->

S = 7161

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Answered by talasilavijaya
0

Answer:

The sum of the terms in the given geometric series is -2387.

Step-by-step explanation:

Geometric series:

  • A geometric series is the series of terms in which the ratio between each pair of successive terms is constant.
  • The series is given by

        a + ar + ar^2 + ar^3+...

  • The nth term is given by ar^{n-1 }
  • Sum of n terms in geometric series is given by
  • S_n = \dfrac{a(1-r^n )}{ 1-r}
  • where a is the first number in the series, r is the common ratio and n is the number of the terms in the series.

Given the geometric series:

7-14+28-...-3584

Here, a=7 , r=-2 and \mbox{nth term} = -3584

To find the number of terms in the given series, use the nth term,  

ar^{n-1 }=-3584

\implies 7\times (-2)^{n-1 }=-3584

\implies  (-2)^{n-1 }=-\dfrac{3584}{7} =-512

\implies  2^{n-1 }=512

Taking log on both sides

n-1=\dfrac{log512}{log2} =\dfrac{2.7092}{0.3010}=9

\implies n=9+1=10

Then, the sum of the terms in the given geometric series is

S_n = \dfrac{a(1-r^n )}{ 1-r}=\dfrac{7\big(1-(-2)^{10}\big )}{ 1-(-2)}

    =\dfrac{7\big(1-1024 )}{ 3}=\dfrac{-7161}{ 3}=-2387

Therefore, the sum of the terms in the given geometric series is -2387.

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