How do you evaluate #cos(7/6 pi)#? Trigonometry Right Triangles Trigonometric Functions of Any Angle 1 Answer A. S. Adikesavan Apr 22, 2016 #- cos(pi/6)=-sqrt 3/2#. Explanation: Cosine in the third quadrant is negative. #cos (pi + theta ) = -cos theta#. Here, #cos ((7pi)/6)=cos(pi+pi/6)=-cos pi/6=-sqrt 3/2#. 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 8639 views around the world You can reuse this answer Creative Commons License