A) (a-b)/(a^1/2-b^1/2)=(a^1/2-b^1/2)*(a^1/2+b^1/2)/(a^1/2-b^1/2)=a^1/2+b^1/2;
б) (z-8)/(z^2/3+2z^1/3+4)= (z^1/3-2)(z^2/3+2z^1/3+4)/(z^2/3+2z^1/3+4)=z^1/3-2;
в) (x^1/2-4)/(x-16)=(x^1/2-4)/(x^1/2-4)(x^1/2+4)= 1/(x^1/2+4);
г) (a+b)/(a^2/3-a^1/3b^1/3+b^2/3)= (a^1/3+b^1/3)(a^2/3-a^1/3b^1/3+b^2/3)/(a^2/3-a^1/3b^1/3+b^2/3)= a^1/3+b^1/3.