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Simple trigonometry question

  1. Oct 6, 2012 #1
    I need to find the length AD. I thought that with the numbers given, and angle A worked out to being 70o there would be two different ways of working length AD out. I thought 8sin20 and 8cos70 would both be acceptable ways of calculating the length but they give different values. Where have I gone wrong?


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  3. Oct 6, 2012 #2
    They don't give different values.
  4. Oct 6, 2012 #3
    My calculator gives 8cos70 = 5.067 and 8sin20 = 7.304.
  5. Oct 6, 2012 #4
    just realised it was in raidians mode. Whoops!
  6. Oct 6, 2012 #5


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    and you should realize (hopefully quickly) that if cos60o=1/2 then cos70o must be less than half, so there is no way 8cos70o > 5, and similarly with sin20o :wink:
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