a) (√3-3)/(√5-√15) = (√3-3)/(√5-√3*√5) = (√3-3)/(√5(1-√3)) = (√3-3)/(-√5(√3-1)) = -(3-√3)/(√5(√3-1)) = -(√3(√3-1))/(√5(√3-1)) = -√3/√5 = -√(3/5) = -√15/5
б) 8/(√6+√2) = (8(√6-√2))/((√6+√2)(√6-√2)) = (8(√6-√2))/(6-2) = (8(√6-√2))/4 = 2(√6-√2) = 2√6-2√2
Ответ: a) -√15/5; б) 2√6-2√2