解(1)原式=5√12×√18
=5×2√3×3√2
=(5×2×3)×(√3×√2)
=30×√(3×2)
=30√6
(2)原式=√5×√3÷√27
=√(5×3÷27)
=√(5/9)
=(√5)/3
(3)原式=-6√45×(-4√48)
=-6×3√5×(-4×4√3)
=[-6×3×(-4)×4]×(√5×√3)
=288×√(5×3)
=288√15
(4)原式=(1/4)√(12a)÷√(3a)
=(1/4)×√(12a÷3a)
=(1/4)×√4
=(1/4)×2
=1/2