Exterior tangent is a geometric term, which means that a circular or spherical object just touches the outer surface of another object. When the radius or diameter of one object is equal to the surface of another object, it is called circumscribed. In geometry, circumscribed is a very important concept, because it can be used to calculate the relationship between two geometric figures, such as the position relationship between two circles, the contact point between two balls and the position relationship between two polygons.

In our daily life, we often encounter the phenomenon of external cutting. For example, when we stick bricks on the wall, in order to be beautiful and accurate, we need to stick bricks on the wall to ensure that the contact points of each brick with adjacent bricks and walls are circumscribed. For another example, when we fix the tire on the wheel, we also need to ensure that the contact point between the tire and the wheel is circumscribed, so as to ensure the stability and safety of the vehicle.

Exterior tangent is also widely used in mathematics and physics. For example, when we calculate the relative position of two planets, we need to consider their circumscribed relationship. In mechanical engineering, when we design robots, automatic production lines and other equipment, we also need to consider the circumscribed relationship of each part to ensure the safety, stability and efficiency of robots and equipment.