Reason: AB=DC, ∠ Abe =∠DCE, ∠AEB=∠DEC,

Get △ Abe △ DCE

∴BE=CE，

∴△BEC is an isosceles triangle;

(2) Tree diagram:

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All possible outcomes (① ②) (① ③) (① ④) (② ①) (② ③) (② ④) (③ ①) (③ ②) (③ ②) (③ ④) (④ ①) (④ ②) (④ ③)

It can also be expressed in the following table:

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It can be seen from the table (or tree diagram) that the equation has 12 possible results on two pieces of paper, and their possibilities are equal, and four results cannot form an isosceles triangle, so the probability that △BEC cannot form an isosceles triangle is.