Twice pi over three radians makes a hundred and twenty degrees.
*** * ***** ***** *****
* * ** * * * * * *
* *** * * * * * * * *
*** * * * * * * * * *****
* * * * * * *
*** * * ***** * * * *
^^^^^^^^^ * ***** * *
**** ***** * * * *
* * * * *
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* * * * * *
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Start sweeping on X axis of quadrant S; sweep
anti-clockwise. A sweep angle of 120 deg.
(sweep arm is marked in x's, angle measurement
in *'s) is in quadrant A. This means your sine
measurement, whatever it is, is POSITIVE.
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The sine value of 120 degrees is approximately
.866
Arc functions are REVERSE functions. CAVEAT: they
IGNORE angles greater than 90. You will get two
possible values out of an arc function if you know
the polarity of x.
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. ^^^^^^^^^^^^^
Here's a table:
Function | Quadrant | Result
^^^^^^^^^|^^^^^^^^^^|^^^^^^^^
_arc_cos_|____S_____|___neg.__|
_arc_cos_|____A_____|___pos.__|
_arc_cos_|____T_____|___neg.__|
_arc_cos_|____C_____|___pos.__|
_arc_sin_|____S_____|___pos.__|
_arc_sin_|____A_____|___pos.__|
_arc_sin_|____T_____|___neg.__|
_arc_sin_|____C_____|___neg.__|
_arc_tan_|____S_____|___neg.__|
_arc_tan_|____A_____|___pos.__|
_arc_tan_|____T_____|___pos.__|
_arc_tan_|____C_____|___neg.__|
o The arc sine of (the sine of [twice pi over three radians] or
[one hundred and twenty degrees]) is either [thirty degrees or
o o pi sixths] or [one hundred and twenty degrees or twice pi thirds].