Question

三角形诱导公式tan（π/2＋α）＝－cotα cot（π/2＋α）＝－tanα 请问在π/2上,tan是无定义的,用t

Answer 1

tan（π/2＋α）= sin（π/2＋α）/ cos（π/2＋α）

= sin[π/2-(-α）]/cos[π/2-(-α）]

= cos(-α)/sin(-α) = cosα/(-sinα)=－cotα

cot（π/2＋α可以同理证明得到.