Trigonometry Proving

• -Wanderer-

  15 Aug 09, 00:59

  Hi! Can someone help me solve this question:

  Use the law of cosines and sin(A) = sin (B+C) to show the law of sines, i.e.

  sin(A)/a = sin(B)/b = sin(C)/c

• HyuugaNeji

  15 Aug 09, 01:16

  http://jwilson.coe.uga.edu/EMT668/EMAT6680.2001/Mealor/EMAT%206700/law%20of%20sines/Law%20of%20Sines%20proof%201/lawofsinesproof1details.html

• -Wanderer-

  16 Aug 09, 03:30

  Originally posted by HyuugaNeji:

  http://jwilson.coe.uga.edu/EMT668/EMAT6680.2001/Mealor/EMAT%206700/law%20of%20sines/Law%20of%20Sines%20proof%201/lawofsinesproof1details.html

  
  Sorry but I don't see how this uses the cosine rule to prove the sine rule...

• wee_ws

  17 Aug 09, 08:32

  Hi,

    I find it odd to prove the sine rule via the cosine rule.

    The sine rule can be proven very simply by comparing the vertical components of two triangles, by dropping a perpendicular from a vertex to its opposite side.

    The cosine rule can be proven by applying Pythagoras' Theorem.

    Thanks!

  Cheers,
  Wen Shih