[Solution] In (1) isosceles trapezoid ABCD, AB=DC,? B=？ DCB, ∫△DFC are isosceles triangles. DCB=？ FCE，

DC=CF, so? B=？ FCE, AB=CF, it is easy to prove that the quadrilateral ABFC is a parallelogram.

(2) Hint: The inverse theorem of the projective theorem cannot be directly used in the senior high school entrance examination, and must be proved by similar triangles.

The angle is 90? .