If the square is 15 units on each side, then its diagonal would be √(15²)+(15)²=√450=15√2 ☺☺☺☺
Let 
and 
. Then
and
The expression under the square root can be rewritten as
Recall that
so that
and assuming 
and 
, we end up with
so that
as required.
Answer: 15 centimeters
Step-by-step explanation: You cut the rectangle into two triangles following the diagonal. You add 12 squared (144) and 9 squared (81) together. You get 225. You get the square root of 225 which is 15 and that is your answer. Basic solving for the hypotenuse.
