E: Solve({(x + b)^(2) + y^(2) = d_{1}^(2), (x - b)^(2) + y^(2) = d_{2}^(2), d_{1} + d_{2} = L}, {d_{1}, d_{2}, y})
ell: Substitute(y, E(2))
¥¦§¨©ª: Substitute(ell, {L = 5, b = 2})