Write the Sum Without Sigma Notation and Evaluate It $$\sum _ { \mathrm { k } = 1 } ^ { 3 } ( - 1 ) ^ { \mathrm { k } + 1 } \cos 10 \mathrm { k } \pi$$

question 201

Multiple Choice

Write the sum without sigma notation and evaluate it.
- $$\sum _ { \mathrm { k } = 1 } ^ { 3 } ( - 1 ) ^ { \mathrm { k } + 1 } \cos 10 \mathrm { k } \pi$$

• A) \(- \cos 10 \pi + \cos 20 \pi - \cos 30 \pi = - 1\)
• B) \(\cos 10 \pi + \cos 30 \pi = 2\)
• C) \(\cos 10 \pi - \cos 20 \pi + \cos 30 \pi = 1\)
• D) \(\cos 10 \pi - \cos 20 \pi + \cos 30 \pi = - 1\)