Choose d, let the midpoint of e and f be d, connecting CD, CE and cf, because ABC is an isosceles right triangle, CD is perpendicular to AB, angle ECF is equal to ECD plus d cf, angle ECD is equal to DCF, AC is equal to BC is equal to A, it is easy to find out, and the tangent value of angle ECD is 1/3, so the tangent value of angle ECF is 3/4.