Thread: trigo-sum
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Old June 17th, 2009, 08:37 PM
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Quote:
Originally Posted by pickslides View Post
you need to evaluate cos(\frac{\pi}{9})

To do this you need to consider cos(a\pm b) = cos(a)\times cos(b)\mp sin(a)\times sin(b)

where cos(\frac{\pi}{9}) = cos(a\pm b)

only after finding this will you be able to get an exact value
This technique will not work in this instance.


Edit: The off-topic discussion regarding the value of questions like this one can be found here: 18th century questions in the 21st century. Any further discussion of this nature should be continued at that thread.
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