How to determine if lines are perpendicular in coordinate geometry
Math Open Reference

Circumscribed rectangle (or bounding box) is the smallest rectangle that contains all of a given set of points in coordinate geometry
Math Open Reference

Interactive examples and theorems
Math Warehouse

Theorems and interactive practice problems.
Math Warehouse

Different Types of Quadrilaterals and their attributes
Math Warehouse

Definition and properties of a parallelogram. Includes a great picture.
Math Open Reference

Gives a great definition of a kite and its properties along with an interactive picture.
Math Open Reference

Gives a great definition of a rhombus and its properties along with an interactive picture.
Math Open Reference
