How do you evaluate $arccos (-1/3)$ ?

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Answer 1 · 2015-11-28T18:34:08

Think of the line $y=-1/3$ crossing the cosine function as shown below. Where the two functions intersect, is the solution ...

The arccos function is only valid over the range $[0,pi]$ .

Below is a graph of the two functions. As you can see, the two functions intersect at $x~~1.911$ radians between $[0,pi]$ .

Using a trigonometry calculator , you can also enter the inverse cosine at $-1/3$ and get more accuracy:

$arccos(-1/3)=1.91063324$ radians

Hope that helps

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Answer 2 · 2015-11-29T00:07:49

Evaluate arccos (-1/3)

Ans: $+- 109.47$

Use calculator.
$cos x = -1/3$ --> arc $x = +- 109^@47$

How do you evaluate arccos (-1/3)arccos (-1/3)?