How do you find the value of #cos (-90)#? Trigonometry Right Triangles Trigonometric Functions of Any Angle 1 Answer sankarankalyanam Apr 18, 2018 #cos- theta = cos (360 - theta) = cos theta color(maroon)(" since cos is +ve in IV Quadrant"# #:. cos (-90) = cos (360 - 90) = cos 90 = 0# Answer link Related questions How do you find the trigonometric functions of any angle? What is the reference angle? How do you use the ordered pairs on a unit circle to evaluate a trigonometric function of any angle? What is the reference angle for #140^\circ#? How do you find the value of #cot 300^@#? What is the value of #sin -45^@#? How do you find the trigonometric functions of values that are greater than #360^@#? How do you use the reference angles to find #sin210cos330-tan 135#? How do you know if #sin 30 = sin 150#? How do you show that #(costheta)(sectheta) = 1# if #theta=pi/4#? See all questions in Trigonometric Functions of Any Angle Impact of this question 14362 views around the world You can reuse this answer Creative Commons License