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Sum the terms of the following series:

[tex]\[ 1+\frac{2}{2}+\frac{3}{2^2}+\frac{4}{2^3}+\cdots \][/tex]


Sagot :

Certainly! Let's analyze the series provided: [tex]\( 1 + \frac{2}{2} + \frac{3}{2^2} + \frac{4}{2^3} + \cdots \)[/tex].

We are asked to sum the first few terms of this series. Let's denote each term of the series as [tex]\( a_n \)[/tex], where [tex]\( n \)[/tex] represents the position of the term in the series. In general, the [tex]\( n \)[/tex]-th term [tex]\( a_n \)[/tex] of this series is given by:

[tex]\[ a_n = \frac{n}{2^{n-1}} \][/tex]

Now, we will identify the number of terms to sum. We will sum the first 10 terms of the series. Here are the first 10 terms calculated individually:

1. For [tex]\( n = 1 \)[/tex]:
[tex]\[ a_1 = \frac{1}{2^{1-1}} = \frac{1}{1} = 1 \][/tex]

2. For [tex]\( n = 2 \)[/tex]:
[tex]\[ a_2 = \frac{2}{2^{2-1}} = \frac{2}{2} = 1 \][/tex]

3. For [tex]\( n = 3 \)[/tex]:
[tex]\[ a_3 = \frac{3}{2^{3-1}} = \frac{3}{4} = 0.75 \][/tex]

4. For [tex]\( n = 4 \)[/tex]:
[tex]\[ a_4 = \frac{4}{2^{4-1}} = \frac{4}{8} = 0.5 \][/tex]

5. For [tex]\( n = 5 \)[/tex]:
[tex]\[ a_5 = \frac{5}{2^{5-1}} = \frac{5}{16} = 0.3125 \][/tex]

6. For [tex]\( n = 6 \)[/tex]:
[tex]\[ a_6 = \frac{6}{2^{6-1}} = \frac{6}{32} = 0.1875 \][/tex]

7. For [tex]\( n = 7 \)[/tex]:
[tex]\[ a_7 = \frac{7}{2^{7-1}} = \frac{7}{64} = 0.109375 \][/tex]

8. For [tex]\( n = 8 \)[/tex]:
[tex]\[ a_8 = \frac{8}{2^{8-1}} = \frac{8}{128} = 0.0625 \][/tex]

9. For [tex]\( n = 9 \)[/tex]:
[tex]\[ a_9 = \frac{9}{2^{9-1}} = \frac{9}{256} = 0.03515625 \][/tex]

10. For [tex]\( n = 10 \)[/tex]:
[tex]\[ a_{10} = \frac{10}{2^{10-1}} = \frac{10}{512} = 0.01953125 \][/tex]

To obtain the sum of these terms, we add them together:

[tex]\[ 1 + 1 + 0.75 + 0.5 + 0.3125 + 0.1875 + 0.109375 + 0.0625 + 0.03515625 + 0.01953125 \][/tex]

Adding these values, we get:

[tex]\[ 1 + 1 = 2 \\ 2 + 0.75 = 2.75 \\ 2.75 + 0.5 = 3.25 \\ 3.25 + 0.3125 = 3.5625 \\ 3.5625 + 0.1875 = 3.75 \\ 3.75 + 0.109375 = 3.859375 \\ 3.859375 + 0.0625 = 3.921875 \\ 3.921875 + 0.03515625 = 3.95703125 \\ 3.95703125 + 0.01953125 = 3.9765625 \][/tex]

Therefore, the sum of the first 10 terms of the series [tex]\( 1 + \frac{2}{2} + \frac{3}{2^2} + \frac{4}{2^3} + \cdots \)[/tex] is:

[tex]\[ \boxed{3.9765625} \][/tex]