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?
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Hi $\displaystyle 0 \leq 120 \leq 180$ therefore $\displaystyle Arccos\left(-\frac12\right) = 120\: deg$
Originally Posted by mj.alawami 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? Hi mj, Cosine is negative in QII and QIII. Cos 120 = -1/2. The angle in QIII would be Cos(240) = -1/2
Last edited by masters; Apr 8th 2009 at 10:45 AM.
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