sin 15° = sin (45°- 30°) = sin 45°× cos 30°- sin 30°×cos 45° = √2/2×√3/2-1/2×√2/2 = √6/4-√2/4
⇒ sin 15° = (√6-√2)/4.
sin 75° = sin (45°+30°) = sin 45°×cos 30° + sin 30°× cos 45° = √2/2×√3/2+1/2×√2/2 = √6/4+√2/4
⇒ sin 75° = (√6+√2)/4.
dar sin 30°=1/2; cos 30°=√3/2 si sin 45°=cos 45°=1/√2=√2/2
deci valoric inseamna:
sin 15° + sin 75° = (√6-√2)/4+(√6+√2)/4 = 2√6/4 = √6/2
sin 15° + sin 75° =√6/2
