Let a cm be the length of the side,then the length of the corresponding altitude is 2a cm (a > 0).The area of the triangle is :

\(\dfrac{a.2a}{2}=100\Leftrightarrow a^2=100\Leftrightarrow a=10\Leftrightarrow2a=20\) 

Hence,the answer is 20 cm or 0,2 m