How do you find the exact values of costheta and tantheta when sintheta=-2/3? Trigonometry Right Triangles Relating Trigonometric Functions 1 Answer Nghi N ยท Shwetank Mauria Dec 30, 2016 costheta= +- sqrt5/3 and tantheta=+- (2sqrt5)/5 Explanation: Use trig identity: cos^2 theta = 1 - sin^2 theta cos ^2theta = 1 - 4/9 = 5/9 cos theta = +- sqrt5/3 tan theta = sintheta/(cos theta) = +- (2/3)(3/sqrt5) = +- 2/sqrt5 = +- (2sqrt5)/5 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 1333 views around the world You can reuse this answer Creative Commons License