(√18+√5)×√10
=√18×√10+√5×√10
=√(18×10)+√(5×10)
=√(6²×5)+√(5²×2)
=6√5+5√2
(4√3-2√6)÷2√3
=4√3÷2√3-2√6÷2√3
=2-√(6÷3)
=2-√2
(5√15-√3/5)×√5
=5√15×√5-√(3/5)×√5
=5√(15×5)-√(3/5×5)
=5√(5²×3)-√3
=5×5√3-√3
=25√3-√3
=24√5
(√80-√90)÷√5
=√80÷√5-√90÷√5
=√(80÷5)-√(90÷5)
=√16-√18
=√4²-√(3²×2)
=4-3√2