Intersection /Interpenetration

When two 3D shapes like cylinders, cones, prisms or pyramids pass through each other, they create intersection lines where their surfaces meet. Think of it like this: when a round pipe (cylinder) goes through a square box (prism), the pipe doesn't simply disappear into the box—instead, it creates a specific line pattern on both shapes showing exactly where they touch and cut through each other.

In Nigeria, you see this happening with drainage pipes passing through building walls, or when ventilation ducts penetrate roof structures on industrial sites. The intersection line is what you must draw accurately on your exam paper.

To find these lines, imagine slicing both solids with horizontal or vertical cutting planes, then mark where each plane cuts both shapes. Where these cutting points align, you plot your intersection line. Practice this method repeatedly with different solid combinations.