Дано: a = 2, b = 4, c = $$3\sqrt{2}$$.
$$l_c = \frac{1}{a+b} \sqrt{ab((a+b)^2 - c^2)}$$
Подставим значения a, b и c в формулу:
$$l_c = \frac{1}{2+4} \sqrt{2 \cdot 4((2+4)^2 - (3\sqrt{2})^2)}$$
$$l_c = \frac{1}{6} \sqrt{8(36 - 18)}$$
$$l_c = \frac{1}{6} \sqrt{8 \cdot 18}$$
$$l_c = \frac{1}{6} \sqrt{144}$$
$$l_c = \frac{1}{6} \cdot 12 = 2$$
Ответ: 2