Answer:
the missing length is 14 unit.
Step-by-step explanation:
Using the Pythagorean Theorem:  For right angle triangle,
Sum of the squares of the two side = Square of longest side    i.e,
 a² + b² = c²                  ......[1]
In the given right triangle:
we are given the measurements for the hypotenuse, c = 50 unit, and one leg, b= 48 unit. 
The hypotenuse is always opposite the right angle and it is always the longest side of the triangle.
To find the length of leg a:
Putting the values of b and c in equation [1];
 or
 or
 or
 or
 unit
 unit
∴  
 
⇒ a= 14 unit
Therefore, the missing length a is ,  14 unit