13. 2(x² + 4) = 4(x² + 2)

$$ \begin{aligned} 2(x^2 + 4) &= 4(x^2 + 2) \\ 2x^2 + 8 &= 4x^2 + 8 \\ 2x^2 - 4x^2 &= 8 - 8 \\ -2x^2 &= 0 \\ x^2 &= 0 \\ x &= 0 \end{aligned} $$

Ответ: x = 0