As shown in the figure, in △ ABC, take AB AC as the edge and make equilateral △ abd △ ace outward respectively. Given DC = 10, find the length of be and explain the reason

As shown in the figure, in △ ABC, take AB AC as the edge and make equilateral △ abd △ ace outward respectively. Given DC = 10, find the length of be and explain the reason

BE=10.
reason:
In equilateral triangle, ad = AB, AC = AE, ∠ DAB = ∠ CAE = 60 °
Then, DAB + BAC = CAE + BAC, that is, DAC = BAE
Then △ DAC ≌ △ BAE (edge)
Then be = DC = 10