I try to find X from the cosine formula but it doesn't sound right

12sq = 8 sq + 5sq - 2x 8x 5cosX

144 = 64 + 25 - 80cosX

55 = -80cosX

x= cos^-1(-55/80)

I keep getting 2.328837092

Please help

Results 1 to 5 of 5

- October 27th 2010, 02:34 PM #1

- Joined
- Jul 2010
- Posts
- 85

- October 27th 2010, 02:44 PM #2

- Joined
- Aug 2007
- From
- USA
- Posts
- 3,111
- Thanks
- 2

- October 27th 2010, 03:04 PM #3

- Joined
- Jul 2010
- Posts
- 85

- October 27th 2010, 03:41 PM #4

- October 29th 2010, 02:02 PM #5

- Joined
- Apr 2005
- Posts
- 16,816
- Thanks
- 1968

If you are thinking about x as being an angle ("cosine" is a function- just because you talk about cos(x) it does not necessarily mean that x is and angle) then x= 2.3288...

**radians**.

Since radians corresponds to 180 degrees, 2.3288 radians= 2.3288 (180/3.14159)= 133.433... degrees.