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walter9906
find Cos 2A, cos A= √3/4
Use the following formula: \[\cos 2A=2\cos ^{2}A-1\] \[\cos 2A=(2\times (\frac{\sqrt{3}}{4})^{2})-1=you\ can\ calculate\]
cos2A=2cos2A−1 put cos A= √3/4 so cos2A=2*(√3/4)*(√3/4)-1