Judgement theorem of two planes perpendicular and its application and understanding of some concepts of dihedral angle. In mathematics, intersection is a relationship between two geometric figures. The intersection of two graphs means that they have a common part, or the point sets belonging to both graphs are not empty sets. If there is only one intersection point between two geometries, it is called tangency rather than intersection.
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In Euclidean geometry, there are four relationships between two circles on the same plane: separation, tangency, compatibility and intersection. Separation means that two circles do not intersect, and neither circle is in the other circle. Tangency means that two circles have only one intersection. Intersection means that two circles have more than one intersection. Compatibility means that two circles do not intersect and one circle is inside the other.
Two circles intersect if and only if the distance between the centers of the two circles is strictly smaller than the sum of the radii of the two circles and strictly larger than the difference between the radii of the two circles. On the Euclidean plane, two straight lines are either parallel, intersect or coincide. This is the inference of Euclid's fifth postulate. Two intersecting straight lines have exactly one intersection point. In non-Euclidean geometry, it can be divided into two categories according to geometric characteristics (curvature).
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