How do you express #cos((27pi)/8)# as a trig function of an angle in Quadrant I? Trigonometry Right Triangles Relating Trigonometric Functions 1 Answer Nghi N Feb 28, 2017 #- cos ((3pi)/8)# Explanation: On the unit circle, #cos ((27pi)/8) = cos ((11pi)/8 + 2pi) = cos ((11pi)/8) = # #= cos ((3pi)/8 + pi) = - cos ((3pi)/8)# Answer link Related questions What does it mean to find the sign of a trigonometric function and how do you find it? What are the reciprocal identities of trigonometric functions? What are the quotient identities for a trigonometric functions? What are the cofunction identities and reflection properties for trigonometric functions? What is the pythagorean identity? If #sec theta = 4#, how do you use the reciprocal identity to find #cos theta#? How do you find the domain and range of sine, cosine, and tangent? What quadrant does #cot 325^@# lie in and what is the sign? How do you use use quotient identities to explain why the tangent and cotangent function have... How do you show that #1+tan^2 theta = sec ^2 theta#? See all questions in Relating Trigonometric Functions Impact of this question 16064 views around the world You can reuse this answer Creative Commons License