Trigonometry Examples

Find the Cosine of the Angle -(2pi)/3
Step 1
Take the cosine of .
Step 2
Add full rotations of until the angle is greater than or equal to and less than .
Step 3
Apply the reference angle by finding the angle with equivalent trig values in the first quadrant. Make the expression negative because cosine is negative in the third quadrant.
Step 4
The exact value of is .