How do you express #tan((19pi)/5)# as a trig function of an angle in Quadrant I? Trigonometry Right Triangles Relating Trigonometric Functions 1 Answer Nghi N Dec 9, 2017 #- tan (pi/5)# Explanation: #tan ((19pi)/5) = tan (-pi/5 + 20pi/5) = tan (-pi/5 + 4pi) = # #= tan (- pi/5) = - tan (pi/5)# #pi/5# is an arc (or angle) in Quadrant 1. 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 2927 views around the world You can reuse this answer Creative Commons License