(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.

Results 1 to 3 of 3

- Mar 8th 2009, 01:14 AM #1

- Joined
- Nov 2008
- Posts
- 607

## 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.

- Mar 8th 2009, 01:49 AM #2

- Joined
- Mar 2009
- Posts
- 66

- Mar 8th 2009, 03:37 AM #3