trig

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inverse cos (-rad2/2)=135 degrees
inverse sin (-rad2/2)=-45 degrees

I don't understand why cos is 135

  • trig -

    for the cosine = -sqrt 2/2 negative x axis
    means quadrant 2 or quadrant 3
    It could be either 180 + 45 or 180 - 45
    so either 135 or 225
    for the sine = -sqrt 2/2
    means quadrant 3 or quadrant 4
    that is 180 + 45 or 360 - 45
    so either 225 or 315

    225 satisfies both the sine and the cosine.

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