Question #ce9db Trigonometry Right Triangles Relating Trigonometric Functions 1 Answer Binayaka C. Aug 16, 2016 #cos 3theta=44/125=0.352# Explanation: #sin theta=3/5 ; cos theta=sqrt(1-(3/5)^2)=4/5# # costheta =-4/5# when #theta# is in between #90^0 & 180^0# #cos 3theta=4cos^3theta-3costheta= 4*(-4/5)^3-3*(-4/5) = -256/125+12/5=44/125=0.352#[Ans] 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 1332 views around the world You can reuse this answer Creative Commons License