How do you evaluate sine, cosine, tangent of $-pi/2$ without using a calculator?

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Answer 1 · 2017-01-23T19:03:04

$"please look at animation below."$

$"first ,let us draw a unit circle. A unit circle is a circle with radius of 1."$

enter image source here

$" if "alpha=0, " then cosine=1, sine=0, tangent=0"$

enter image source here

$"if alpha="-pi/2 " then cosine=0, sine=-1, tangent="(-1)/0" undefined"$

enter image source here

How do you evaluate sine, cosine, tangent of -pi/2-pi/2 without using a calculator?