a) \(5\sqrt{a}-4b\sqrt{25a^3}+5a\sqrt{16ab^2}-2\sqrt{9a}\)
=\(5\sqrt{a}-4b.5a\sqrt{a}+5a.4b\sqrt{a}-2.3\sqrt{a}\)
=\(5\sqrt{a}-20ab\sqrt{a}+20ab\sqrt{a}-6\sqrt{a}\)
=\(5\sqrt{a}-6\sqrt{a}=-\sqrt{a}\)
b) \(5a\sqrt{64ab^3}-\sqrt{3}.\sqrt{12a^3b^3}+2ab\sqrt{9ab}-5b\sqrt{81a^3b}\)
=\(5a.8b\sqrt{a}-6ab\sqrt{ab}+2ab.3\sqrt{ab}-5b.9a\sqrt{b}\)
=\(40ab\sqrt{ab}-6ab\sqrt{ab}+6ab\sqrt{ab}-45ab\sqrt{ab}\)
=\(-5ab\sqrt{ab}\)
câu b) bước 2 sửa lại chút
\(5a.8b\sqrt{ab}-6ab\sqrt{ab}+6ab\sqrt{ab}-5a.9b\sqrt{ab}\)