√(9/4 -√2)
=√(2+1/4 -√2)
=√ [ (√2)^2 +(1/2)^2 -2 *√2 *1/2]
=√ (√2 - 1/2)^2
=√2 - 1/2
即化简得到
√(9/4 -√2) =√2 - 1/2