How do you find the exact value of sin(-90)? Trigonometry Right Triangles Trigonometric Functions of Any Angle 1 Answer sankarankalyanam Mar 7, 2018 sin (-90) = -1 Explanation: sin -90 = sin (360 - 90) = sin 270 Angle 270^@ is third quadrant, where only tan and cot are positive. Hence sin 270 = sin (180 + 90) = - sin 90 = -1 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 55392 views around the world You can reuse this answer Creative Commons License