Geometry: Area, Volume & the Coordinate Plane

What you’ll learn

• Area uses square units; volume uses cubic units. Never mix them in one answer.
• Compose or decompose polygons into rectangles and triangles, then add (or subtract) their areas.
• Triangle area is $A = \tfrac{1}{2}bh$ with **perpendicular** height; parallelogram area is $A = bh$.
• On the coordinate plane, horizontal side length is $|x_1 - x_2|$; vertical side length is $|y_1 - y_2|$ when edges align with the axes.
• Volume of a right rectangular prism is $V = \ell wh$, even when edge lengths are fractions.
• A net shows all faces of a prism flat; a box net has six rectangular faces that pair up when folded.