Answer:
15
Step-by-step explanation:
[tex]using \: pythagoras \: theorem \\ let \: the \: unknown \: side = x \\ 25 {}^{2} = x {}^{2} + 20 {}^{2} \\ 625 = x {}^{2} + 400 \\ x {}^{2} = 625 - 400 \\ x {}^{2} { = 225} \\ x = \sqrt{225} \\ x = 15 \\ lenght \: of \: the \: third \: side = 15[/tex]
