Two sides of a triangle have the following measures . find the range of possible measures for the tird side

To find the third side you would use Pythagorean theorem which is a²+b²=c². 

A and B being the 2 legs and C being the hypotenuse.
 
Example: ( sorry for the really odd not really a triangle, triangle...)
  |  \
6|     \  ?                    6²+9²=C²
  |              36+81=C²
        9                             117=C²
                               √117=10.8 (rounded) 

if you need to get the leg you just fill in the numbers.

They can measure  the amount of energy gained or lost

Density and pressure