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Aratati ca cos 20 grade+cos 50 grade-sin 70 grade-sin 40 grade=0

Răspuns :

cos 20°+cos 50°-sin 70°-sin 40°=0
cos(90°-20°)+cos(90°-50°)-sin 70°-sin 40°
sin 70°+sin 40°-sin 70°-sin 40°
sin 110°-sin 70°- sin 40°
sin 40° -sin 40° =0