a)\(A=\sqrt{12}+3\sqrt{27}-5\sqrt{48}\)
\(=\sqrt{2^2.3}+3\sqrt{3^2.3}-5\sqrt{4^2.3}\)
\(=2\sqrt{3}+9\sqrt{3}-20\sqrt{3}\)\(=-9\sqrt{3}\)
b)\(B=3\sqrt{a^2+3}-3\sqrt{16a^2+48}+4\sqrt{25a^2+75}\)
\(=3\sqrt{a^2+3}-3\sqrt{16\left(a^2+3\right)}+4\sqrt{25\left(a^2+3\right)}\)
\(=3\sqrt{a^2+3}-12\sqrt{a^2+3}+20\sqrt{a^2+3}\)\(=11\sqrt{a^2+3}\)