2√5 + 4 ------------- = 2√5 - 4

(2√5 + 4)/(2√5 - 4) x (2√5 + 4)/(2√5 + 4)
= (4√25 + 8√5 + 8√5 + 16)/(4√25 - 16)
= (4.5 + 16√5 + 16)/(4.5 - 16)
= (20 + 16√5 + 16)/(20-16)
= (36 + 16√5)/4
= 9 + 4√5