中四級數學-三角學(1)

please read: http://postimg.org/image/qyiqae40t/

圖片參考：https://s.yimg.com/lo/api/res/1.2/6dIJx4QXdUo.kbjIieCDoA--/YXBwaWQ9dHdhbnN3ZXJzO3E9ODU-/http://s30.postimg.org/rba4gkman/QQ_20140413141458.jpg


圖片參考：https://s.yimg.com/lo/api/res/1.2/YQchnsnIEm2D.fssQFQsTg--/YXBwaWQ9dHdhbnN3ZXJzO3E9ODU-/http://s30.postimg.org/qyiqae40t/QQ_20140413141458.jpg

http://www.fss.edu.hk/maths/formula/trigonometry.htm

http://www.fss.edu.hk/maths/formula/trigo%20II.htm

請先看意見欄的教學:
https://hk.knowledge.yahoo.com/question/question?qid=7014040900101

(a)

-1/tanθ = (5 - sinθ)/(-cosθ)

1/tanθ = (5 - sinθ)/cosθ

cosθ/sinθ = (5 - sinθ)/cosθ

cos²θ = (5 - sinθ)sinθ

1-sin²θ = 5sinθ - sin²θ

5 sinθ = 1

2014-04-13 13:54:53 補充：
(b)

先乘分母過左邊, 變成 (a) 的模樣~

用 (a) 的結果:

5 sinθ = 1

sinθ = 1/5

θ = 11.536959° or 180°-11.536959°