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Topic: cos 120 is -0.5 or -0.3?  (Read 5248 times)

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Offline Prof.Zzz

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cos 120 is -0.5 or -0.3?
« on: September 30, 2017, 02:46:50 AM »
When I am doing character table calculation for IR active bands, I have the formula: 1+2cos Φ
if the angel is 120 it says that the value is zero, but in my calculater 1+2cos 120 equal to 0.38
how can they get cos 120 equal to -0.5? I want to know how to do it with calculater in case I encounter different angel Φ value
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Offline Borek

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Re: cos 120 is -0.5 or -0.3?
« Reply #1 on: September 30, 2017, 03:37:44 AM »
Hard to tell what you are doing wrong, there are thousands of calculators and zillions of ways of incorrectly keying the formula into each of them.

Definitely [itex]cos(120) = -\frac 1 2[/itex].
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Offline sjb

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Re: cos 120 is -0.5 or -0.3?
« Reply #2 on: September 30, 2017, 03:48:43 AM »
cos 120° = -1/2

But maybe you're in radians, or some other degree measure?
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