How to Find the Area of the Intersection of Two Polygons
GeoMaster on the TI84 graphing calculator can’t find the area of a polygon formed by the intersection of two other polygons because GeoMaster doesn’t know that it’s there. To get GeoMaster to find the area of the intersection, you must use GeoMaster to define the polygon formed by this intersection.
To do this, you first find the points of intersection of the sides of the original two polygons. And then you use these points to get GeoMaster to define the polygon formed by the intersection. But this is not as easy as it seems because GeoMaster is not capable of finding the points of intersection of two polygons.

Use the Segment tool ([GRAPH][WINDOW][3]) to construct segments over the intersecting sides of the polygons.

Use the Intersection tool ([GRAPH][WINDOW][ALPHA][PRGM]) to find the points of intersection of the segments constructed in Step 1.

Use the Polynomial tool ([GRAPH][WINDOW][6]) to construct the polygon formed by the intersection of the original polygons.

Use the Area tool ([GRAPH][ZOOM][2]) to find the area of the polygon formed by the intersection of the original polygons.