tan -105 等于多少以及 计算过程

1/2 = sin30 = 2 sin15 cos15
√3/2 = cos30 = 1 - 2 (sin15)^2
tan15 = sin15/cos15 = (1 - √3/2)/(1/2) = 2-√3
tan(-105) = - tan105 = - cot(-15) = cot15 = 1/tan15 = 2+√3