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Please help!

 May 8, 2020
 #1
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First    sec = 1/ cos      to have a negative sec   cos must be negative (Q II and III)

- 2 sqrt 3/3  is the same as  -2/sqrt 3    and this is   1/ cos

     so cos (3x) = -sqrt 3/2

               3x = 5pi/6     and    7pi/6     

                  x = 5 pi/18            7 pi/18

 May 9, 2020

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