How do you evaluate sine, cosine, tangent of -840^circ without using a calculator?

1 Answer
Nghi N.
Feb 18, 2017

sin = - sqrt3/2
cos = - 1/2
tan = sqrt3

Explanation:

Trig unit circle gives:
sin (-840) = sin (-120 - 720) = sin (-120) = - sin (-120 + 180) = - sin (60).
Trig table of special arcs gives:
sin (-840) = - sin (60) = - sqrt3/2
cos (-840) = cos (- 120) = cos (120) = - 1/2
tan (-840) = sin/(cos) = (- sqrt3/2)(- 2/1) = sqrt3

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