1. It is known that the bisector of ∠BAD in quadrilateral ABCD intersects BC at point E ∠ the bisector of ∠ADC intersects BC at point F. Proof: BF=CE2. It is known that the bisector of ∠BAD in quadrilateral ABCD intersects BC at point E ∠ the bisector of ∠ADC intersects BC at point F AB=5, BC=8. Find the long figure of line segment EF:

1. In quadrilateral ABCD, diagonal AC and BD intersect at point O. It is known that the circumference of △BOC is 3CM larger than that of △AOB, and the circumference of quadrilateral ABCD is 26CM. Find the length of BC. 2. In quadrilateral ABCD, diagonal AC and BD are at point O. It is known that the difference between the perimeter of △BOC and that of △AOB is 3CM, and the perimeter of quadrilateral ABCD is 20 cm. Supplement to the long BC question: In fact, the so-called "quadrangles" are all parallelograms = = (because the original title is drawn with symbols, it is quadrangles ORZ) Questioners: anonymous best answer 1, ∫ ad ‖ BC ∴∠ DAE = ∠ BEA ∠ DAE = ∠. It feels like a parallelogram ABCD. If the quadrilateral ABCD is a parallelogram, we can get: (Ob+OC+BC)-(OA+Ob+AB) = 3. Because OA = OC ∴ BC-AB = 3,2 (BC+AB) = 26, we can get: BC = 8, AB = 5. The latter question is exactly the same as this one.