[tex] x\in \mathbb_{N} $ \\ \\ 1)$ $\dfrac{x}{2} = \dfrac{8}{x} \Rightarrow x^2 = 16 \Rightarrow x = 4 \\ \\ 2) $ $ \dfrac{3}{x} = \dfrac{x}{12} \Rightarrow x^2 = 3\cdot 12\Rightarrow x^2 = 36 \Rightarrow x = 6 \\ \\ 3) $ $ \dfrac{x}{3} = \dfrac{27}{x} \Rightarrow x^2 = 3\cdot 27\Rightarrow x^2 = 81 \Rightarrow x = 9 \\ \\ 4) $ $ \dfrac{20}{x} = \dfrac{x}{5} \Rightarrow x^2 = 5\cdot 20\Rightarrow x^2 = 100 \Rightarrow x = 10 [/tex]
[tex]5) $ $ \dfrac{x}{4} = \dfrac{9}{x} \Rightarrow x^2 = 9\cdot 3\Rightarrow x^2 = 36 \Rightarrow x = 6 \\ \\ [/tex]
