2. \(\sqrt{9a}+\sqrt{25a}-\sqrt{36a}\)

При \(a\geqslant0\):

\(\sqrt{9a}=3\sqrt{a}\), \(\sqrt{25a}=5\sqrt{a}\), \(\sqrt{36a}=6\sqrt{a}\).

Тогда:

\(3\sqrt{a}+5\sqrt{a}-6\sqrt{a}=2\sqrt{a}\).

Ответ: \(2\sqrt{a}\)