tan15度
=sin15/cos15
=sin(45-30)/cos(45-30)
=(sin45cos30-cos45sin30)/(cos45cos30+sin45sin30)
=[(根号6-根号2)/4]/[(根号6+根号2)/4]
=[(根号6-根号2)(根号6-根号2)]/[(根号6+根号2)(根号6-根号2)]
=(6-4根号3+2)/(6-2)
=2-根号3
tan75= (1-cos 150°)/sin150°
=2+ 根号3
tan15度
=sin15/cos15
=sin(45-30)/cos(45-30)
=(sin45cos30-cos45sin30)/(cos45cos30+sin45sin30)
=[(根号6-根号2)/4]/[(根号6+根号2)/4]
=[(根号6-根号2)(根号6-根号2)]/[(根号6+根号2)(根号6-根号2)]
=(6-4根号3+2)/(6-2)
=2-根号3
tan75= (1-cos 150°)/sin150°
=2+ 根号3