√15+√35+√21+5／√3+2√5+√7 =(√3+√5)(√5+√7)/(√3+√5+√5+√7) =1/(1/(√3+√5)+1/(√5+√7)) =2/(√5-√3+√7-√5) =2/(√7-√3) =(√7+√3)/2
