13. 2(x^2 + 4) = 4(x^2 + 2)

Решим уравнения: 13. $2(x^2 + 4) = 4(x^2 + 2) \implies 2x^2 + 8 = 4x^2 + 8 \implies 2x^2 = 0 \implies x = 0$ 14. $(x - 2)^2 - 8 = 0 \implies (x - 2)^2 = 8 \implies x - 2 = \pm\sqrt{8} \implies x = 2 \pm 2\sqrt{2}$ 15. $9x^2 - 1 = 0 \implies 9x^2 = 1 \implies x^2 = \frac{1}{9} \implies x = \pm\frac{1}{3}$ 16. $3x - 2x^2 = 0 \implies x(3 - 2x) = 0 \implies x_1 = 0, x_2 = 1,5$ 17. $x^2 = 3x \implies x^2 - 3x = 0 \implies x(x - 3) = 0 \implies x_1 = 0, x_2 = 3$ 18. $x^2 + 2x - 3 = 2x + 6 \implies x^2 = 9 \implies x = \pm 3$ 19. $3x^2 + 7 = 12x + 7 \implies 3x^2 - 12x = 0 \implies 3x(x - 4) = 0 \implies x_1 = 0, x_2 = 4$ 20. $3x^2 - 48 = 0 \implies 3x^2 = 48 \implies x^2 = 16 \implies x = \pm 4$ 21. $3x^2 - 12 = 0 \implies 3x^2 = 12 \implies x^2 = 4 \implies x = \pm 2$ 22. $2x^2 + 6x = 0 \implies 2x(x + 3) = 0 \implies x_1 = 0, x_2 = -3$ 23. $1,8x^2 = 0 \implies x = 0$ 24. $x^2 + 9 = 0 \implies x^2 = -9$. Корней нет (в действительных числах). 25. $7x^2 - 14 = 0 \implies 7x^2 = 14 \implies x^2 = 2 \implies x = \pm\sqrt{2}$