In mathematics, a ratio is a relationship between two numbers indicating how many times the first number contains the second. So, in this case our numbers are the two legs of a triangle. Given that this is a right triangle because one angle is equal to 90, the the relations are as follows:


In the figure below α = 30, so


There are two ratios:

 and
 
 Therefore:
 
  
 Finally, matching these results with the image above, the ratio:

is the only one that apply