12.9) 0,4⁴⁻⁵ˣ = 0,16√0,4

Решим уравнение:

$$0.4^{4-5x} = 0.16 \sqrt{0.4}$$

$$0.4^{4-5x} = (0.4)² \cdot (0.4)^{1/2}$$

$$0.4^{4-5x} = 0.4^{2 + 1/2}$$

$$0.4^{4-5x} = 0.4^{5/2}$$

$$4 - 5x = \frac{5}{2}$$

$$8 - 10x = 5$$

$$10x = 3$$

$$x = \frac{3}{10} = 0.3$$

Ответ: 0.3