(3√2+√48)(√18-4√3)
=(3√2+4√3)(3√2-4√3)
=18-12√6+12√6-48
=-30
(√a+√b)^2-(√a-√b)^2
=(√a+√b+√a-√b)(√a+√b-√a+√b)
=(2√a)*(2√b)
=4√(ab)