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 purpose of finding a coterminal angle when evaluating trigonometric functions?

• To increase the angle's magnitude

• To simplify the calculation by finding an equivalent angle within one revolution

• To change the trigonometric function being evaluated

• To avoid using the unit circle

How can you convert 2π into a fraction with a common denominator to add it to -, 9π / 4?

• Multiply 2π by 3/3

• Multiply 2π by 8/8

• Multiply 2π by 4/4

• Multiply 2π by 2/2

What is the coterminal angle of -, 9π / 4 after adding 2π?

• 3π / 4

• -π / 4

• π / 4

• -3π / 4

In which quadrant is the angle -, π / 4 located?

• Third Quadrant

• First Quadrant

• Fourth Quadrant

• Second Quadrant

What is the cosine value of the angle -, π / 4?

• 0

• 1

• sqrt 2 / 2

• -sqrt 2 / 2