How do you evaluate #cos ((7 pi)/3 + (15 pi)/4)#? Trigonometry Right Triangles Trigonometric Functions of Any Angle 1 Answer A. S. Adikesavan Jun 4, 2016 #=(sqrt 3+1)/(2 sqrt 2)# Explanation: #cos ((7pi)/3+(15pi)/4)# #=cos (2pi+pi/3 + 4pi-pi/4)# #=cos(6pi+(pi/3--pi/4))# #=cos (pi/3-pi/4)# #=cos(pi/3)cos(pi/4)+sin(pi/3)sin(pi/4)# #=(1/2)(1/sqrt 2)+(sqrt 3/2)(1/sqrt 2)# #=(sqrt 3+1)/(2 sqrt 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 1316 views around the world You can reuse this answer Creative Commons License