How do you evaluate sine, cosine, tangent of #-pi/2# without using a calculator? Trigonometry Right Triangles Trigonometric Functions of Any Angle 1 Answer ali ergin Jan 23, 2017 #"please look at animation below."# Explanation: #"first ,let us draw a unit circle. A unit circle is a circle with radius of 1."# #" if "alpha=0, " then cosine=1, sine=0, tangent=0"# #"if alpha="-pi/2 " then cosine=0, sine=-1, tangent="(-1)/0" undefined"# 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 6221 views around the world You can reuse this answer Creative Commons License