AlexThadunny AlexThadunny
  • 21-11-2016
  • Mathematics
contestada

if cos2X=1/3 and 0<=2X<=pi, find cosX ...?

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HomertheGenius
HomertheGenius HomertheGenius
  • 24-11-2016
cos 2 X = 1/3
cos 2 X = cos ² X - sin² X
cos ² X - sin ² X = 1/3
+
cos ² X + sin ² X = 1
------------------------------
2 cos ² X = 4/3    / : 2
cos ² X = 2/3  
cos X = √2/3  ( angle X is in the 1st quadrant )
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