Question 711151
 as per  pythagoras theorem 



 side ^2 + side ^2  = hypotenuse ^2 
  3^2 + missing  side ^2  = 5^2 
  9 + missing side ^2  = 25
   missing side ^2    = 25-9
        missing side  ^2  =16
         missing side  = sqrt (16) 
                        = 4 cm

 answer = 4 cm