babydoll332
Evaluate sec 240° without using a calculator by using ratios in a reference triangle.



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butterflyprincess
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unit circle??

babydoll332
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with outt it

hartnn
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ok, u know what is cos 60 ?

babydoll332
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pi/3

hartnn
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cos pi/3 = ?

babydoll332
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60

hartnn
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lol!
60=pi/3
cos 60 = 0.5
ok ?

babydoll332
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ohh ok

hartnn
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sec 240 = 1/ cos 240
cos 240 = cos (180+60)
cos (180+x) = cos x
now try

babydoll332
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what should i try im a lilttle confused

hartnn
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cos (180+x) = cos x
so
cos 240 = cos 60 = 0.5
got this ?

babydoll332
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i think so

hartnn
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now sec 240 =1/ cos 240 = 1/(0.5) = 2
ok ?

babydoll332
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why did u use cos 60 though?

ByteMe
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60 degrees is the reference angle for 240 degrees

hartnn
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because cos 60 is known
60 is standard angle
in unit circle

babydoll332
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ok

hartnn
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any more doubts ?