有一个谜语:有一样东西,看不见、摸不着,但它却无处不在,请问它是什么?谜底是:空气。而数学,也像空气一样,看不见,摸不着,但它却时时刻刻存在于我们身边。如果在一个图形上能找到一条直线,将这个图形沿着这条直线对折可以使两边完全重合,这样的图形就叫做轴对称图形,这条直线叫做对称轴。如果仔细观察,可以发现飞机是一个标准的轴对称物体,俯视看,它的机翼、机身、机尾都呈左右对称。轴对称使它飞行起来更平稳。 There is a riddle: there is one thing, invisible, touching, but it is everywhere, what is it? The answer is: the air. And mathematics, like the air, can not see or touch, but it always exists in our side. If you can find a straight line on a graph, fold the graph straight along the line so that the two sides completely coincide. Such a graph is called an axisymmetric graph. This line is called an axis of symmetry. If you look closely, you can see that the aircraft is a standard axisymmetric object, looking down, its wings, fuselage, tail are bilaterally symmetrical. Axisymmetric makes it fly more smoothly.