(根号6-5)(根号2+根号3)
=(√6-5)(√2+√3)
=√6×√2+√6×√3-5×√2-5×√3
=√(6×2)+√(6×3)-5√2-5√3
=√(2²×3)+√(3²×2)-5√2-5√3
=2√3+3√2-5√2-5√3
= -3√3-2√2
(根号54+根号24-2根号15)除以根号3
=(√54+√24-2√15)÷√3
=√54÷√3+√24÷√3-2√15÷√3
=√(54÷3)+√(24÷3)-2√(15÷3)
=√18+√8-2√5
=√(3²×2)+√(2²×2)-2√5
=3√2+2√2-2√5
=5√2-2√5