If angle x is an acute angle and cos x = t, how do you express cos (180 - x) in terms of t? Trigonometry Right Triangles Relating Trigonometric Functions 1 Answer Konstantinos Michailidis May 27, 2016 Remember that #cos(A-B)=cosA*cosB+sinA*sinB# hence #cos(180-x)=cos180*cosx+sinx*sin180=(-1)*cosx+sinx*0= -cosx=-t# Finally #cos(180-x)=-t# 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 2353 views around the world You can reuse this answer Creative Commons License