Explicație pas cu pas:
a)
[tex]\frac{x}{12} = \frac{3}{x} \iff {x}^{2} = 12 \times 3 \\ {x}^{2} = 36 \implies \bf x = 6 [/tex]
b)
[tex]\frac{16}{x} = \frac{x}{25} \iff {x}^{2} = 16 \times 25 \\ {x}^{2} = 400 \iff {x}^{2} = {20}^{2} \\ \implies \bf x=20[/tex]
c)
[tex] \frac{x}{2 \sqrt{5} } = \frac{ \sqrt{45} }{x} \iff {x}^{2} = 2 \sqrt{5} \times \sqrt{45} \\ {x}^{2} = 2 \sqrt{5} \times 3 \sqrt{5} \iff {x}^{2} = 30 \\ \bf x = \sqrt{30} [/tex]
