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September 17, 2014

September 17, 2014

Posted by **Master chief** on Tuesday, June 7, 2011 at 4:26pm.

arccos(-1/2)

- trig -
**Reiny**, Tuesday, June 7, 2011 at 5:12pmyou want the angle Ø so that

cosØ= -1/2

We know that if the cosØ is negative, then Ø is in either the II or III quadrant

we also know that cos 60° =+1/2

so Ø = 180-60 or 180+60

Ø = 120° or 240°

in radians it would be 2π/3 or 4π/3

your calculator will only give you the angle closest to the origin,

inter

2nd

cos

-.5

=

and you will get 120 if your calculator is set to degrees.

- trigononometry -
**aron**, Friday, June 17, 2011 at 7:52am(12x2.17)

cos0 120.6

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