Discover a world of knowledge at Westonci.ca, where experts and enthusiasts come together to answer your questions. Experience the ease of finding quick and accurate answers to your questions from professionals on our platform. Discover detailed answers to your questions from a wide network of experts on our comprehensive Q&A platform.

Please I need some help!!!!!!!
The sum of the series \(\sum_{i^{-1}}^{10}5\left(\frac{1}{2}\right)^i\) is \(\frac{x}{1,024}\).

Then x =_______.


Sagot :

It looks like you're given

[tex]\displaystyle \sum_{i=1}^{10} 5 \left(\frac12\right)^i = \frac{x}{1024}[/tex]

Consider the geometric sum,

[tex]\displaystyle S = \sum_{i=1}^{10} \left(\frac12\right)^i[/tex]

[tex]S = \dfrac12 + \dfrac1{2^2} + \dfrac1{2^3} + \cdots + \dfrac1{2^{10}}[/tex]

Multiply both sides by 1/2 :

[tex]\dfrac12 S = \dfrac1{2^2} + \dfrac1{2^3} + \dfrac1{2^4} + \cdots + \dfrac1{2^{11}}[/tex]

Subtract this from S :

[tex]S - \dfrac12 S = \dfrac12 - \dfrac1{2^{11}}[/tex]

Solve for S :

[tex]\dfrac12 S = \dfrac12 - \dfrac1{2^{11}}[/tex]

[tex]S = 1 - \dfrac1{2^{10}}[/tex]

[tex]S = \dfrac{2^{10} - 1}{2^{10}}[/tex]

[tex]S = \dfrac{1023}{1024}[/tex]

The given sum is just 5 times S, so x = 1023 × 5 = 5115.