Find the length of the third side. If necessary, write in simplistic radical form.

By Pythagoras theorem
[tex]H ^{2} = P^{2} + B ^{2} [/tex]
[tex]( \sqrt{65} ) ^{2} = P ^{2} + 4 ^{2} [/tex]
[tex]65 = P^{2} + 16[/tex]
[tex]P^{2} = 65 - 16[/tex]
[tex]P^{2} = 49[/tex]
[tex]P= \sqrt{49} [/tex]
[tex]P = 7[/tex]