Teorema de Pitágoras:
[tex]h {}^{2} = c {}^{2} + c {}^{2} \\ \\ 25 {}^{2} = 20 {}^{2} + x {}^{2} \\ \\ 625 = 400 + x {}^{2} \\ \\ - x {}^{2} = 400 - 625 \\ \\ - x {}^{2} = - 225 \: \: \: . \: ( - 1) \\ \\ x {}^{2} = 225 \\ \\ x = \sqrt{225} \\ \\ \boxed{\boxed{\boxed{x = 15}}} \\ [/tex]
