kill(all);

van=facebook.com/LearningCalculus$

U:[1, 2]$ V:[3, 1]$

f(x,y,a,b):= x^2/a^2 + y^2/b^2= 1$

e1: f(U[1], U[2], a, b);

e2: f(V[1], V[2], a, b);

a: sqrt(rhs(first(solve((e1-4*e2),a^2))));

b: sqrt(rhs(first(solve((9*e1-e2),b^2))));