Answer:
1
Explanation:
The side ratios of a 30-60-90 triangle are 1 : √3 : 2, so any one side is sufficient to determine the other two.
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Additional comment
The length of one side is sufficient, but you do need to know which side it is. You cannot just say, for example, "one side is 5 units." Rather, you must say something like "the shortest side is 5 units", or "the side between the largest angles is 5 units" so its relation to the other sides is known.