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how to prove sin(18\(^\circ\)) =  \(\cos (4 \cdot 18^{\circ})\) using right triangle or unit circle 

 Feb 5, 2022
 #1
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You can use exponential notation.

 Feb 5, 2022
 #2
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ok, let me try. 

Dennis070sinneD  Feb 5, 2022
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Forget about that first suggestion.  It was a nonsense answer.

 

Draw a right angle tiangle with one angle of 18degrees.  Work out what the other anglw will have to be.

 

Call the hypotenuse h and the other two sides x and y.

 

Now use the trianlge to prove, or at least convince youself and anyone looking over your shoulder, that is is true :)

 Feb 5, 2022

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