Wolfram Research
Wolfram Math World: Area
Definitions and formulas for the computation of surface areas of triangles, rectangles, and any regular polygon. Helpful links to related pages.
Analyze Math
Analyze Math: Area of Triangles
The geometry resource explores the different formulas used to calculate the area of triangles. The applet investigates the angles and sides of a triangle.
Cuemath
Cuemath: Cosine Law
A comprehensive guide for learning all about the law of cosine with definitions, what is the law, and solved examples.
Math Open Reference
Math Open Reference: Area of an Equilateral Triangle
Learn about the area of an equilateral triangle with this helpful reference tool. Provides a detailed definition, examples, and an internet activity that enhances further explanation. Includes links to related topics.