5) 72+x.74-5x = \frac{1}{49}

5) 7^2+x⋅7^4-5x = $$\frac{1}{49}$$

$$7^{2 + x + 4 - 5x} = \frac{1}{7^2}$$

$$7^{6 - 4x} = 7^{-2}$$

$$6 - 4x = -2$$

$$-4x = -2 - 6$$

$$-4x = -8$$

$$x = -8 : (-4)$$

$$x = 2$$

Ответ: $$x = 2$$