document.write( "Question 577615: What's the Exact Value for Sin 390 degrees ? Without using a calculator \n" ); document.write( "

Algebra.Com's Answer #370222 by KMST(5328) $\"\"$ $\"About$

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$\"390%5Eo=360%5Eo%2B30%5Eo\"$ , so $\"sin%28390%5Eo%29=sin%2830%5Eo%29\"$ .
\n" ); document.write( " $\"sin%2830%5Eo%29=1%2F2\"$ .
\n" ); document.write( "I remember that, but I can also prove it out of a right triangle:
\n" ); document.write( "Suppose you have a right triangle ABC, with the right angle at C and a $\"30%5Eo%29\"$ angle at A. That triangle is half of an equilateral triangle.
\n" ); document.write( "

so $\"sin%2830%5Eo%29=sin%28BAC%29=BC%2FAB=1%2F2\"$ \n" ); document.write( "

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