[00:00:00] Trigonometric Functions - 南9不是娇?
[00:07:00] When you first study math about 1234
[00:10:00] First study equation about xyzt
[00:12:00] It will help you to think in a logical way
[00:14:00] When you sing sine cosine tangent
[00:16:00] Sine cosine tangent cotangent
[00:18:00] Sine cosine secant cosecant
[00:20:00] Let\'s sing a song about trig-functions
[00:23:00] sin(2π+α)=sinα
[00:24:00] cos(2π+α)=cosα
[00:27:00] tan(2π+α)=tanα
[00:29:00] Which is induction formula1 and induction formula 2
[00:31:00] sin(π+α)=-sinα
[00:33:00] cos(π+α)=-cosα
[00:35:00] tan(π+α)=tanα
[00:37:00] sin(π-α)=sinα
[00:39:00] cos(π-α)=-cosα
[00:42:00] tan(π-α)=-tanα
[00:44:00] These are all those \"name do not change\"
[00:46:00] As pi goes to half pi the difference shall be huge
[00:48:00] sin(π/2+α)=cosα
[00:50:00] sin(π/2-α)=cosα
[00:52:00] cos(π/2+α)=-sinα
[00:54:00] cos(π/2-α)=sinα
[00:57:00] tan(π/2+α)=-cotα
[00:59:00] tan(π/2-α)=cotα
[01:43:00] You wanna measure width of a river height of a tower
[01:45:00] You scratch your head which cost you more than an hour
[01:47:00] You don\'t need to ask any \"gods\" or\" master\" for help
[01:49:00] This group of formulas are gonna help you solve
[01:51:00] sin(α+β)=sinα•cosβ+cosα•sinβ
[01:54:00] cos(α+β)=cosα•cosβ-sinα•sinβ
[01:58:00] tan(α+β)=(tanα+tanβ)/(1-tanα•tanβ)
[02:02:00] sin(α-β)=sinα•cosβ-cosα•sinβ
[02:05:00] cos(α-β)=cosα•cosβ+sinα•sinβ
[02:08:00] tan(α-β)=(tanα-tanβ)/(1+tanα•tanβ)
[02:12:00] As you come across a right triangle you feel easy to solve
[02:16:00] But an obtuse triange gonna make you feel confused
[02:18:00] Don\'t worry about what you do
[02:19:00] There are always means to solve
[02:20:00] As long as you master the sine cosine law
[02:25:00] At this moment I\'ve got nothing to say
[02:30:00] As trig-functions rain down upon me
[02:34:00] At this moment I\'ve got nothing to say
[02:38:00] Let\'s sing a song about trig-functions
[02:43:00] Long live the trigonometric functions