kill(all)$

van=facebook.com/LearningCalculus$

a(x,y):=(diff(y,x,2)^(-1))$
b(x,y):=(-diff(y,x,2)^(-1)*diff(y,x)^-3)$
c(x,y):=(diff(y,x,2)*diff(y,x)^-2)$
d(x,y):=(-diff(y,x,2)*diff(y,x)^-3)$
e(x,y):=(diff(x,y,2))$

a(x,x^2);

b(x,x^2);

c(x,x^2);

d(x,x^2);

e(sqrt(y),y);

substitute(x^3,y^(3/2),%);