题目

One of the first signs visitors encounter（遇见）at most museums is“Please do not touch the exhibits”. However at the new Hoy tocael Prado exhibition at Madrid’s Museo Nacional Del Prado, the officials don’t just encourage the habit, they insist upon it. That’s because this art display has been specially created to enable visually(视觉的) impaired(受损) patrons（顾客）to experience the joy of the works of some of the world’s most famous artists just like able-bodied people can. The 3-D masterpieces(杰作)is the idea of Estudios Durero. The creators began by 如图，点M、N分别在正方形ABCD的边BC、CD上，△MCN的周长等于正方形ABCD周长的一半，求∠MAN的度数．