BBC
Bbc: Area in General
You can pick up some valuable pointers on how to find the area of a triangle, rectangle, and other quadrilaterals. When you finish working your way through the pages you can take an on-line "Test Bite," and check your understanding.
Math Planet
Math Planet: Geometry: Parallelogram, Triangles Etc
Resource examines the area of geometric solids through examples and a video lesson. [0:39]
Wolfram Research
Wolfram Math World: Rhombus
This math site explains properties of the rhombus, gives a visual aid to help with the formula given for it's area.
Quia
Ixl Learning: Rhombuses
Brush up on your math skills relating to rhombuses then try some practice problems to test your understanding.
Quia
Ixl Learning: Parallelograms
Brush up on your math skills pertaining to parallelograms then try some practice problems to test your understanding.
Ministry of Education and Universities of the Region of Murcia (Spain)
Ministerio De Educacion Y Ciencia: Figuras Geometricas en El Plano
Interactive activities dealing with the areas of quadrilaterals figures.
Varsity Tutors
Varsity Tutors: Hotmath: Algebra Review: Rhombus
Find a quick, concise explanation of a rhombus. An example is given and clearly explained.
Math Open Reference
Math Open Reference: Quadrilaterals
A complete reference guide to quadrilaterals including squares, rectangles, parallelograms, trapezoids, and rhombus. It provides definitions and interactive activities that enhance further explanation.
Wolfram Research
Wolfram Math World: Squares
MathWorld provides multiple definitions and formulas for the mathematical term, square.
BBC
Bbc: Bitesize: Maths: 2 D Shapes
Learn about the properties of 2-D shapes: circles, triangles, polygons, and quadrilaterals. Includes information, video, and examples about each, with games and quizzes for reinforcement.