[00:00.00]trigonometric functions - 爱迪生
[00:00.10]词：天儿
[00:00.19]曲：天儿
[00:00.28]Cosine cosine tangent
[00:01.59]Sine cosine tangent cotangent
[00:03.76]Sine cosine secant cosecant
[00:05.93]Let's sing a song about trig-functions
[00:08.07]sin（2π+α）=sinα
[00:09.92]cos（2π+α）=cosα
[00:11.97]tan（2π+α）=tanα
[00:14.34]Which is induction formula1 and induction formula 2
[00:16.57]sin（π+α）= —sinα
[00:18.82]cos（π+α）=—cosα
[00:20.90]tan（π+α）= tanα
[00:22.88]sin（π－α）= sinα
[00:25.04]cos（π－α）=－cosα
[00:27.17]tan（π－α）=－tanα
[00:29.44]These are all those name do not change
[00:31.46]As pi goes to half pi the difference shall be huge
[00:33.91]sin（π/2+α）=cosα
[00:35.69]sin（π/2－α）=cosα
[00:37.88]cos（π/2+α）=－sinα
[00:40.06]cos（π/2－α）=sinα
[00:42.08]tan（π/2+α）=－cotα
[00:44.14]tan（π/2－α）=cotα