It is known that each edge length of oblique triangular prism abc-a1b1c1 is 1, and the angle a1ab = angle a1ac = 60 degrees How to prove bcc1b1 as a square

It is known that each edge length of oblique triangular prism abc-a1b1c1 is 1, and the angle a1ab = angle a1ac = 60 degrees How to prove bcc1b1 as a square

Because the angle a1ab = angle a1ac = 60 °, the photography of A1 on the bottom is that the angle bisector of ∠ cab passes through AI point and makes a1o ⊥ on the bottom, that is, a1o ⊥ on BC. Take the midpoint of BC as Q to connect AQ, so AQ ⊥ on BC, that is, Ao is perpendicular to BC, so BC is ⊥ on plane a1ao, because B1B ‖ A1A, so B1B is perpendicular to BC, because bcc1b1 is diamond, and because ∠ b1bc = 90 ° it is square