1) $\displaystyle \arccos ( \frac{-1}{2} ) $

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I am getting 120 degrees but should I take 120 degrees or the reference angle which is 60 as the answer?

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- Apr 8th 2009, 09:37 AMmj.alawamiFind the exact value
1) $\displaystyle \arccos ( \frac{-1}{2} ) $

Attempt using the calculator

I am getting 120 degrees but should I take 120 degrees or the reference angle which is 60 as the answer? - Apr 8th 2009, 10:22 AMrunning-gag
Hi

$\displaystyle 0 \leq 120 \leq 180$ therefore $\displaystyle Arccos\left(-\frac12\right) = 120\: deg$ - Apr 8th 2009, 10:24 AMmasters