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cos(−1380)Find an angle that is coterminal to −1380A=60°A=60°Find the value using the definition of cosine.cos(60)=adjacent/hypotenusecos(60)=adjacent/hypotenuseSubstitute the values into the definition.cos(60)=121cos(60)=121Simplify the result.12

The value of cos (-1380°) is 1/2. The correct option is b. 1/2

What is the cosines of negative angles?

From the question, we are to determine the value of cos (-1380°)

Since the sum of angle at a point is 360°, adding 360° to an angle will not change its value

To find the value of the angle, we will add 360° to the angle until we get a positive value

That is,

-1380° + 360° = -1020°

-1020° + 360° = -660°

-660° + 360° = -300°

-300° + 360° = 60°

That means

cos (-1380°) = cos (60°)

From the trigonometry table,

cos (60°) = 1/2

Thus,

cos (-1380°) = 1/2

Hence, the value of cos (-1380°) is 1/2. The correct option is b. 1/2

Learn more on Evaluating cosines of angles here: https://brainly.com/question/44279

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