解法一：cos30 °= √¯3/2 cos15 °= √¯[(1 + cos30° )/2] sin15° = √¯[(1 - cos30° )/2] tan15° = sin15° /cos15° = √¯[(1 - cos30° )/(1 + cos30° )] = √¯[(2 - √¯3)/...