Trinagles can be classified according to sides and angles
Math Open Reference

The conventional method of calculating the area of a triangle (half base times altitude) with pointers to other methods and special formula for equilateral triangles
Math Open Reference

Worksheet to practice classifying triangles as scalene, isosceles, or equilateral.
Helping with Math

In this Early Edge video lesson, you'll learn more about Triangles: Perimeter and Area, so you can be successful when you take on highschool Math & Geometry.
The Princeton Review

In this Early Edge video lesson, you'll learn more about Complementary and Supplementary Angles, so you can be successful when you take on highschool Math & Geometry.
The Princeton Review

In this Early Edge video lesson, you'll learn more about Types of Angles, so you can be successful when you take on highschool Math & Geometry.
The Princeton Review

The worksheets below can be used as part of extra math homework. These geometry worksheets are free and easily printable. They cover typical school work from grade 4 through 8. They include questions on polygons, 3D objects, angles, and calculations of area, volume, etc.
Helping With Math.com

In this Early Edge video lesson, you'll learn more about Equilateral, Isoceles and Scalene Triangles, so you can be successful when you take on highschool Math & Geometry.
The Princeton Review

In this Early Edge video lesson, you'll learn more about Triangles, so you can be successful when you take on highschool Math & Geometry.
The Princeton Review

An introduction the the concept of solving a triangle.
Math Open Reference
