The third question:

Solution: ∫ED is the median vertical line of line segment BC (known).

∴EB=EC (the distance from the point on the middle vertical line to both sides is equal).

∵AC=8cm, the circumference of △ABE is 14cm, and AE+EC = AC.

∴ab=c△abe-ae-be=c△abe-ac= 14-8=6(cm)

Question 4: Sorry, I can't draw. Let me tell you the method: pass through point E and point F respectively and make their perpendicular lines. The intersection point is the point o required by the problem. No, you can try.