According to the existing conditions of the topic, the solution of the topic is uncertain if there is no other explanation. Note that the big topic is "Little Doctor of Mathematics", and it is estimated that the topic is a bit like IQ. Where should the topic hide the mystery? This mystery is a hidden condition. The most likely mystery is that "the vertex of the lower left corner of the small rectangle is on the diagonal of the big rectangle" (of course, the premise is that the big quadrilateral is a rectangle and the blank quadrilateral it contains is also a rectangle. If you insist on saying, "Don't mention the topic." That's nothing to say. ) I think this is more reliable. If you want to say "the topic is not mentioned" again. ",that can't answer.