1/x+√(1/x^2+x^2-2)
=1/x+√(1/x-x)^2
=1/x+|1/x-x|
∵x=2/5
∴1/x>x
∴1/x+|1/x-x|
=1/x+(1/x-x)
=2/x-x
=2/(2/5)-2/5
=5-2/5
=4.6