How do you find the exact value of cos (-5pi/3)? Trigonometry Right Triangles Trigonometric Functions of Any Angle 1 Answer bp Mar 26, 2016 #1/2# Explanation: Start like this #cos ((-5pi)/3) = cos (2pi -(5pi)/3) # because adding #2pi# does not change the value of a trignometric function.So, #2pi-(5pi)/3 = pi/3# #cos ((pi)/3)# equals #1/2# **** Answer link Related questions How do you find the trigonometric functions of any angle? What is the reference angle? How do you use the ordered pairs on a unit circle to evaluate a trigonometric function of any angle? What is the reference angle for #140^\circ#? How do you find the value of #cot 300^@#? What is the value of #sin -45^@#? How do you find the trigonometric functions of values that are greater than #360^@#? How do you use the reference angles to find #sin210cos330-tan 135#? How do you know if #sin 30 = sin 150#? How do you show that #(costheta)(sectheta) = 1# if #theta=pi/4#? See all questions in Trigonometric Functions of Any Angle Impact of this question 7204 views around the world You can reuse this answer Creative Commons License