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

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

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

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

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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 $\displaystyle \pi= 3.14159... $ radians corresponds to 180 degrees, 2.3288 radians= 2.3288 (180/3.14159)= 133.433... degrees.