3)∠AEB is a right angle, which translates into the existence of point E on the circle with diameter AB, that is, the straight line Y = X+T has two intersections with the circle with diameter AB, and the value range of T can be obtained by combining numbers and shapes:

4)∠AFC is a right angle, so we can solve the equation of bisecting AC vertically by a straight line first. If point E exists, the intersection of a straight line and a parabola is point E, and there are two intersections, so it is necessary to verify whether they are both satisfied.