Question #ea04c Trigonometry Right Triangles Trigonometric Functions of Any Angle 1 Answer P dilip_k Mar 21, 2017 #cos (pi/7 )cos ((4pi)/21) - sin (pi/7) sin ((4pi)/21)# #=cos (pi/7 +(4pi)/21) # #=cos( (3pi +4pi)/21) # #=cos( (7pi)/21) # #=cos( (pi)/3) =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 1017 views around the world You can reuse this answer Creative Commons License