(√5-√3+√2)(√5+√3-√2)=[√5-(√3-√2)][√5+(√3-√2)]=(√5)²-(√3-√2)²=5-(5-2√6)=2√6
(√5-√3+√2)(√5+√3-√2)=(√5-√3)(√5+√3)-(√5-√3)√2+(√5+√3)√2-2=5-3+2√6-2=2√6
(a-b+c)(a+b-c)=[a-(b-c)][a+(b-c)]=a^2-(b-c)^2=a^2-(b^2+c^2-2bc)=2*根号6吧