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- March 8th 2009, 12:14 AM #1

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- Nov 2008
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- 600

## cos-1(0) = 90, so cos 90 = 0 but...

(I am talking in degrees)

cos-1(0) = 90 so cos 90 = 0 but cos (-270) and cos 270 and cos (-90) are all also equal to 0. So then WHY does the calculator only give 90 when I do cos-1(0)?

I know that cos (theta) = cos (-theta) by the way.

- March 8th 2009, 12:49 AM #2

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- Mar 2009
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- 66

- March 8th 2009, 01:37 AM #3