Question 750012
The classic pythagorean triangle is 3,4,5 a 3 unit side connected to a 4 unit side and a 5 unit hypotenuse. 

15, 20 is a 3  to 4 ratio, 3*5, then 4*5, the remaining side, the diagonal, is 5*5 or 25. 

3^2+4^2=5^2 and
15^2+20^2=25^2