Arturo O. answered 08/16/17
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As Carol explained in her answer, if all you know is the 3 angles, then all you can get from that is the relative proportions of the 3 sides, so you can express any 2 sides in terms of the 3rd side. Think of it as a matter of scale. Draw a 30-60-90 triangle, and then redraw it twice as large. The 2 triangles are both 30-60-90, but the sides have different lengths. There are infinitely many lengths possible in a 30-60-90 triangle. But if you know any one side, then you can get the other two using Pythagoras' theorem or trigonometry.