Answer:
A) The reference angle should be [tex]\frac{\pi }{3}[/tex], and the sign of the value should be negative.
Step-by-step explanation:
cos([tex]\frac{10\pi }{3}[/tex])
Remove full rotations of 2π until the angle is between 0 and 2[tex]\pi[/tex].
cos([tex]\frac{4\pi }{3}[/tex])
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.
-cos([tex]\frac{\pi }{3}[/tex])
The exact value of cos([tex]\frac{\pi }{3}[/tex]) is [tex]\frac{1}{2}[/tex].
−[tex]\frac{1}{2}[/tex]
