B) 4x2 -1/3 = x(10x-9); г) 3/4x² = 2/5x² +3/4.

B) $$\frac{4x^2 - 1}{3} = x(10x - 9)$$

$$4x^2 - 1 = 30x^2 - 27x$$

$$26x^2 - 27x + 1 = 0$$

$$D = (-27)^2 - 4 \cdot 26 \cdot 1 = 729 - 104 = 625$$

$$x_1 = \frac{27 + \sqrt{625}}{2 \cdot 26} = \frac{27 + 25}{52} = \frac{52}{52} = 1$$

$$x_2 = \frac{27 - \sqrt{625}}{2 \cdot 26} = \frac{27 - 25}{52} = \frac{2}{52} = \frac{1}{26}$$

Ответ: $$x_1 = 1$$, $$x_2 = \frac{1}{26}$$

г) $$\frac{3}{4}x^2 = \frac{2}{5}x^2 + \frac{3}{4}$$

$$\frac{3}{4}x^2 - \frac{2}{5}x^2 = \frac{3}{4}$$

$$\frac{15x^2 - 8x^2}{20} = \frac{3}{4}$$

$$\frac{7}{20}x^2 = \frac{3}{4}$$

$$x^2 = \frac{3}{4} \cdot \frac{20}{7}$$

$$x^2 = \frac{15}{7}$$

$$x_1 = \sqrt{\frac{15}{7}}$$

$$x_2 = -\sqrt{\frac{15}{7}}$$

Ответ: $$x_1 = \sqrt{\frac{15}{7}}$$, $$x_2 = -\sqrt{\frac{15}{7}}$$