Alternatively, use formula for arithmetic series:
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- Evaluate the sum \(\sum_{k=1}^{5} (2k + 1)\).
- Compute each term: when \(k=1\), \(2(1)+1=3\); \(k=2\), \(5\); \(k=3\), \(7\); \(k=4\), \(9\); \(k=5\), \(11\).
- Sum: \(3 + 5 + 7 + 9 + 11 = 35\).
- First term = 3, last term = 11, number of terms = 5.
- Sum = \(\frac{n}{2}(a + l) = \frac{5}{2}(3 + 11) = \frac{5}{2} \times 14 = 35\).
- Find the area of a regular hexagon with side length 6 cm.
