kill(all)$

van=facebook.com/LearningCalculus$

f(a,b):= 1/(a-b)-1/(b-1) = (a-1)/2$
g(a,b):= a^2-b^2 = (a^2+b^2)^(1/3)$

f(x,y);
g(x,y);

x1:rhs(first(solve(f(x,y),x)));
y1:rhs(first(solve(f(x,y),y)));

g(x1,y);
g(x,y1);