分母有理化
1/√(3+2√2)+ 1/(√5+2√6)+1/√(7+4√3)+1/√(9+4√5)
=√(3-2√2)+ √(5+2√6)+√(7-4√3)+√(9-4√5)
=√2-1+√3-√2+√4-√3+√5-√4
=√5-1