How can one find the equation of the locus of the point P, if the points A (1, 2), B (3, 4) are at an equal distance from P? Find the equation of the locus of a point P = (x, y) when the sum of the squares of the distances from P to the points (a, 0) and (-a, 0) is 4b^2, where b >= a/sqrt(2)?