206.
[tex]ax^2-2bx+c = 0,\quad q = 2 \\ \\ a,b,c\,\text{ sunt in progresie geometrica.}\\\\\Rightarrow b = a\cdot q,\quad c = a\cdot q^2\\\\ \\ ax^2-2(a\cdot q)x+(a\cdot q^2) = 0\Big|:a \\ \\ x^2-2qx+q^2 = 0 \\ \\ x^2-4x+4 = 0 \\ \\ (x-2)^2 = 0 \\ \\ \Rightarrow \boxed{x = 2}[/tex]
⇒ b) corect.
