The Wolfram Language provides fully integrated support for plane geometry, including basic regions such as points, lines, triangles, and disks; functions for computing basic properties such as arc length and area; and nearest points to solvers to find the intersection of regions or integrals over regions.
SSSTriangle — a triangle specified by the length of its sides
Graphics — visualize regions with different styles
ArcLength — length of a curve
Area — area of a region
RegionMember — test whether a point is in a region
RegionNearest — nearest point in a region to a given point
FindInstance — find examples of points in a region
Solve — find curve crossings etc.