In Geometry Union is normally used to indicate the combining of several geometric shapes into a single shape.
Consider the example below. The concept of geometric unions is used (incompletely here) to demonstrate why the area of a triangle is ##1/(wh)##
The following geometric union statements are applicable:
##color(white)(XXXX)####squareACDF =triangleAB_1Fuutriangle FBDuutriangleDB_2C##
##color(white)XXXX####triangle BFD = triangle FB_1B_2 = triangle FB_1AuutriangleDB_2C##