1. a/√11 = (a√11)/(√11)^2 = a√11/11;
2. x/(√x-√y) = x•(√х+√у)/((√x-√y)•(√х+√у)) = x(√х+√у)/(х-у).
3. 4/(√5-1) = 4(√5+1)/((√5-1)(√5+1)) = 4(√5+1)/((√5)^2-1) = 4(√5+1)/(5-1) = 4(√5+1)/4 = √5 + 1.
1. a/√11 = (a√11)/(√11)^2 = a√11/11;
2. x/(√x-√y) = x•(√х+√у)/((√x-√y)•(√х+√у)) = x(√х+√у)/(х-у).
3. 4/(√5-1) = 4(√5+1)/((√5-1)(√5+1)) = 4(√5+1)/((√5)^2-1) = 4(√5+1)/(5-1) = 4(√5+1)/4 = √5 + 1.