Answer:
[tex]\displaystyle 8,9[/tex]
Step-by-step explanation:
Deduct one from nine to get eight, then use the Pythagorean Theorem:
[tex]\displaystyle a^2 + b^2 = c^2 \\ \\ 8^2 + 4^2 = x^2 \hookrightarrow 64 + 16 = x^2 \hookrightarrow \sqrt{80} = \sqrt{x^2}; 4\sqrt{5}\:[or\:8,94427191...] = x \\ \\ \boxed{8,9 \approx x}[/tex]
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