Find the Exact Value by Using a Half-Angle Identity $\cos 165 ^ { \circ }$

question 176

Multiple Choice

Find the exact value by using a half-angle identity.
- $\cos 165 ^ { \circ }$

• A) \(- \frac { 1 } { 2 } \sqrt { 2 - \sqrt { 3 } }\)
• B) \(\frac { 1 } { 2 } \sqrt { 2 + \sqrt { 3 } }\)
• C) \(- \frac { 1 } { 2 } \sqrt { 2 + \sqrt { 3 } }\)
• D) \(\frac { 1 } { 2 } \sqrt { 2 - \sqrt { 3 } }\)

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Definitions:

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A question in economics that points out the contradiction between the high value of diamonds, which are non-essential, and the low value of water, which is essential for survival.

Marginal Utility

The extra pleasure or benefit derived from using one more unit of a product or service.

Essential Goods

Goods that are necessary for basic survival and well-being, such as food, water, and healthcare.

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