If #cos theta=4/5#, #0<=theta=<pi/2#, how do you find #sin theta#? Trigonometry Right Triangles Relating Trigonometric Functions 1 Answer Alan P. Nov 16, 2016 #color(green)(sin(theta)=3/5# Explanation: #cos="adjacent"/"hypotenuse"color(white)("XXXXX")sin="opposite"/"hypotenuse"# By the Pythagorean Theorem #color(white)("XXX")"opposite" = sqrt(5^2-4^2)=3# #rArr sin(theta)=3/5# 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 21766 views around the world You can reuse this answer Creative Commons License