Most of the square numbers are even.so if we need to find root over we need an even number to convert it to perfect square.
See the example below
[tex]\\ \ast\bull\rm\longmapsto H^2=P^2+B^2[/tex]
[tex]\\ \ast\bull\rm\longmapsto H^2=3^2+4^2[/tex]
[tex]\\ \ast\bull\rm\longmapsto H^2=9+16[/tex]
[tex]\\ \ast\bull\rm\longmapsto H^2=25[/tex]
[tex]\\ \ast\bull\rm\longmapsto H=\sqrt{25}[/tex]
[tex]\\ \ast\bull\rm\longmapsto H=5[/tex]
Some other triplets are