Solve a high school math problem

Connect AB 1 and BC 1. In the triangular prism ABC-a1b1c1,ab = AC = BC = a1b1= a655438. Extend AB from point B to point D, let BD=AB, and shoot point D in plane A 1B 1C 1, then BD = B1= AB, then BD/. So BD 1=BC 1, while ∠ C 1bd 1 = 60 and BC 1=BD 1, so the triangle BC1d/kloc-0. Connect C 1D 1, in the triangle C 1B 1D 1, c1b1= b1d/kloc-0.