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2014-02-16T13:11:52+02:00
sin 10 grade + sin 30 grade - sin 170 grade = 1/2
sin 170
°=sin (180°-170°)=sin 10°
sin 10°+ sin 30°-sin 10°=(se reduce sin 10° cu -sin 10°) 
=sin 30°=1/2