Answer:
never
Explanation:
In a 30 - 60 - 90 degree triangle , the common ratio is 
1 : 
 : 2
 : 2
Shorter leg that is opposite to 30 degree = 1
Longer leg that is opposite to 60 degree = 

Hypotenuse is opposite to 90 degree = 2
Shorter leg is half the length of the hypotenuse as per the ratio
Long leg is never the half of the hypotenuse