(2+根号5)^2005 * (2-根号5)^2005 +根号20
= (根号5+2)^2005 * [-(根号5-2)^2005] +根号20
= - (根号5+2)^2005 * (根号5-2)^2005 +根号20
= - [(根号5+2) (根号5-2)]^2005 +根号20
= - [5-4]^2005 +根号20
= -1+根号20
= 2根号5 -1
(2+根号5)^2005 * (2-根号5)^2005 +根号20
= (根号5+2)^2005 * [-(根号5-2)^2005] +根号20
= - (根号5+2)^2005 * (根号5-2)^2005 +根号20
= - [(根号5+2) (根号5-2)]^2005 +根号20
= - [5-4]^2005 +根号20
= -1+根号20
= 2根号5 -1