How do you evaluate #2 cos^2 (pi/12) - 1#? Trigonometry Right Triangles Trigonometric Functions of Any Angle 1 Answer Konstantinos Michailidis May 15, 2016 We know that #cos(2x)=2cos^2(x)-1# Hence for #x=pi/12# we have that #2cos^2(pi/12)-1=cos(2*pi/12)=cos(pi/6)=sqrt3/2# 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 7820 views around the world You can reuse this answer Creative Commons License