Using period as an aide to evaluate for cosine

The video tutorial explains how to evaluate the cosine of -9π/4 by finding a coterminal angle. The instructor demonstrates adding 2π to -9π/4 to obtain a smaller angle, -π/4, and explains the importance of common denominators in this process. The tutorial then uses the unit circle to determine the cosine of -π/4, highlighting the reflection of the angle in the fourth quadrant and identifying the cosine as the x-coordinate, which is sqrt(2)/2.

What is the process to find a coterminal angle for -9π/4?

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How do you add a fraction to a whole number when finding a coterminal angle?

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What is the cosine value of -π/4 and how is it derived?

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Explain the significance of the unit circle in evaluating cosine for angles like -π/4.

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What does the reflection of -π/4 in the fourth quadrant imply for its cosine value?

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