`(sqrt{7}+sqrt{5})/(sqrt{7}-sqrt{5}) + (sqrt{7}-sqrt{5})/(sqrt{7}+sqrt{5})`
`=((sqrt{7}+sqrt{5}).(sqrt{7}+sqrt{5}))/((sqrt{7}+sqrt{5}).(sqrt{7}-sqrt{5})`` + ((sqrt{7}-sqrt{5}).(sqrt{7}-sqrt{5}))/((sqrt{7}-sqrt{5}).(sqrt{7}+sqrt{5}))`
`=((sqrt{7}+sqrt{5})^2 )/(7-5) +((sqrt{7}-sqrt{5})^2 )/(7-5)`
`=(7+2.sqrt{7}.sqrt{5}+5)/2` `+` `(7-2.sqrt{7}.sqrt{5}+5)/2`
`=(7+2.sqrt{7}.sqrt{5}+5+7-2.sqrt{7}.sqrt{5}+5)/2`
`=24/2`
`=12`
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