Solution: Draw its profile development diagram, as shown above:

So: must ABCD be a parallelogram and DC? =? CF？ =? AB？ =? Adjutant general

According to the known situation, it can be concluded that: AC? =? 2π

If a is the vertical AE of BC, then: AE? =? 1, and easy to know: CAE? =? ABC？ =? a

So we know: cos? Answer? =? 1/(2π)