how do you find the length of side a if thehypotenuse is c=12 and A is 30 degrees

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It is a special triangle, 30-60-90; therefore the sides have a proportion of 1-2-square root of 3.  The longest side being the hypotenuse and the 2 (2 > 1.73).  Side a is opposite angle A, so it is the short leg (1).  So the answer is (1/2) the hypotenuse or 6.