2.2.2 Calculate the sum of the first 30 even terms of the sequence.

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A convergent geometric series consisting of only positive terms has a first term [tex]$\alpha$[/tex], a constant ratio [tex]$r$[/tex], and an [tex]$n^{\infty}$[/tex] term, [tex]$I_n$[/tex], such that [tex]$\sum^{\infty} I_n = \frac{1}{4}$[/tex].

3.1 If [tex]$I_1 + I_2 = 2$[/tex], write down an expression for [tex]$\alpha$[/tex] in terms of [tex]$r$[/tex].

3.2 Calculate the values of [tex]$\alpha$[/tex] and [tex]$r$[/tex].



Answer :

Alright, let's look at each part of your problem and work through the solutions step by step.

### Problem 2.2.2: Sum of the First 30 Even Terms of a Sequence

To find the sum of the first 30 even terms of a sequence, let's consider the sequence of even numbers:
[tex]\[2, 4, 6, 8, 10, \dots\][/tex]

The formula for the [tex]\(n\)[/tex]-th even number is given by:
[tex]\[a_n = 2n\][/tex]

For the sum of the first 30 even numbers, we can use the formula for the sum of the first [tex]\(n\)[/tex] terms of an arithmetic series:
[tex]\[S_n = \frac{n}{2} (a_1 + a_n)\][/tex]

Where:
- [tex]\(n\)[/tex] is the number of terms.
- [tex]\(a_1\)[/tex] is the first term.
- [tex]\(a_n\)[/tex] is the last term.

So for 30 terms:
- [tex]\(n = 30\)[/tex]
- [tex]\(a_1 = 2\)[/tex]
- [tex]\(a_{30} = 2 \times 30 = 60\)[/tex]

Now, plug these values into the formula:
[tex]\[S_{30} = \frac{30}{2} (2 + 60) = 15 \times 62 = 930\][/tex]

So, the sum of the first 30 even terms is 930.

### Problem 3: Convergent Geometric Series

### Problem 3.1: Expression for [tex]\( \alpha \)[/tex] (First Term) in Terms of [tex]\( r \)[/tex] (Common Ratio)

Given:
1. ∑ I_n from n=1 to ∞ = 1/4
2. I_1 + I_2 = 2

For a geometric series, the sum of infinite terms is given by:
[tex]\[S_\infty = \frac{a}{1 - r} \][/tex]

Here, the sum of the infinite terms is [tex]\(\frac{1}{4}\)[/tex]:
[tex]\[\frac{a}{1 - r} = \frac{1}{4}\][/tex]

It’s known that :
[tex]\[I_1 = a\][/tex]
[tex]\[I_2 = ar\][/tex]
[tex]\[I_1 + I_2 = a + ar = 2\][/tex]
[tex]\[ a(1 + r) = 2 \][/tex]
[tex]\[a = \frac{2}{1 + r}\][/tex]

### Problem 3.2: Calculating the Values of [tex]\( \alpha \)[/tex] and [tex]\( r \)[/tex]

From ∑ I_n from [tex]\(n=1\)[/tex] to ∞ = [tex]\(\frac{1}{4}\)[/tex]:
[tex]\[ \frac{\alpha}{1 - r} = \frac{1}{4} \][/tex]

Substitute [tex]\(\alpha = \frac{2}{1 + r}\)[/tex] into the equation:
[tex]\[ \frac{\frac{2}{1 + r}}{1 - r} = \frac{1}{4} \][/tex]
[tex]\[ \frac{2}{(1+r)(1-r)} = \frac{1}{4} \][/tex]
[tex]\[ \frac{2}{1 - r^2} = \frac{1}{4} \][/tex]
[tex]\[ 8 = 1 - r^2 \][/tex]
[tex]\[ r^2 = -7 \][/tex] which is not possible for positive term.

Hence, let's check secondary option:
[tex]\[ \frac{2}{1 + r + 1 -r} = \frac{1}{4} \][/tex]
[tex]\[ \frac{2}{2} = \frac{1}{4}\][/tex]
[tex]\[ 1 = 1/4\][/tex]

Errors foreseen. Retry:
No possible other simplification to resolve the task if same values.
Remember convergent restriction [tex]\(r^{\rightarrow}\)[/tex].

Thus,
\[ alpha and r. 4th quadratic dependent to adjust.


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