Find the Exact Value cos(-900)

Problem

cos(−900)

Solution

1. Identify the angle in degrees and find its coterminal equivalent within the standard range of 0 to 360

2. Add multiples of 360 to the negative angle until it is positive.

−900+360=−540

−540+360=−180

−180+360=180

3. Determine the cosine of the coterminal angle 180 using the unit circle.

4. Recall that at 180 the coordinates on the unit circle are (−1,0) where the x-coordinate represents the cosine value.

cos(180)=−1

Final Answer

cos(−900)=−1

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