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The question is asking to find the sum of the first 15 terms of an arithmetic sequence where the first few terms are given as:

\[
60, 50, 40, \dots
\]

This is an arithmetic sequence, where:
- The first term \(a = 60\),
- The common difference \(d = 50 - 60 = -10\).

To find the sum of the first 15 terms (\(S_{15}\)), we use the formula for the sum of the first \(n\) terms of an arithmetic sequence:

\[
S_n = \frac{n}{2} \times (2a + (n - 1) \cdot d)
\]

Substituting the values:
- \(n = 15\),
- \(a = 60\),
- \(d = -10\),

\[
S_{15} = \frac{15}{2} \times (2 \cdot 60 + (15 - 1) \cdot (-10))
\]

Now, I will calculate the sum.The sum of the first 15 terms of the arithmetic sequence is \(-150\).

Would you like any further explanation or have any questions?

Here are 5 related questions to expand on this:

1. How do you find the common difference in an arithmetic sequence?
2. What happens to the sum of an arithmetic series if the common difference is positive?
3. How would you calculate the 20th term of this sequence?
4. What is the general form of the \(n\)-th term of an arithmetic sequence?
5. How does the sum of an infinite arithmetic series differ from a finite one?

**Tip:** For an arithmetic sequence, if the common difference is negative, the terms will keep decreasing, which can lead to a negative sum over several terms.

Diketahui deret aritmetika 60 + 50 + 40 + ... Tentukan jumlah 15 suku pertama!

Discover how to calculate the sum of the first 15 terms of an arithmetic sequence starting with 60, 50, and 40, reducing by 10 for each subsequent term. This detailed guide uses the formula S_n = n/2 * (2a + (n - 1) * d) to provide a comprehensive step-by-step solution.

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