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 May 4th 2014, 09:29 PM #1 Junior Member   Join Date: May 2014 Posts: 2 Physics and mathematics Root[2A^2(1 Cos theta)]=root[4A^2 cos^2 theta /2] Could you please explain this.
 May 5th 2014, 05:03 AM #2 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,331 You seem to be missing an important '+' sign, and didn't use parentheses as needed, but I think what you mean is this: To show this is true start by cancelling out the square root sign and 2A^2 from both sides, leaving: Now substitute 2*alpha for theta, and use the double angle formula for cosine: All that remains is some minor rearrangement and resubstitute theta for alpha. Also note that because of the square root signs this is true only for positive values of cos(theta/2): -pi <= theta <= +pi. Last edited by ChipB; May 5th 2014 at 09:30 AM.

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