Notice the relative angle measurements of each riangle. The first triangle above has angle measurements that all less than 90°. For this reason we would call the triangle an acute triangle. If a triangle has a single right angle we appropriately call it a right triangle. Triangle number two fits this definition. When neither of these definitions fit (when one angle is greater than 90°), we call it an obtuse triangle.

We have already identified the three triangles based upon the measure of their angles. Now we can do the same with their side measurement. The first triangle has all three sides of equal length. We know this is true because of the 'tick marks' on each side. Since each side has exactly one tick mark, we infer that all sides are of equal length. We can now call this triangle an acute-equilateral triangle. Notice how we combine the two properties of the triangle. This gives persons who may not be able to see a triangle a better mental picture about what you are describing. The second triangle has only two sides that are equal in length so we would say it is an isosceles triangle. Combining its description based on its angles we would now describe it as a right-isosceles triangle. The third and final triangle has no sides that are equal in measure. Since the triangle has one angle greater than 90° we call it an obtuse-scalene triangle. Refer back to the triangles above and make sure you can identify each by both angle measure as well as side length. Also, try identifying each of the triangles on the chalkboard below.

As you already know, the area of any triangle can be found by the formula A=b*h/2. However, what consitutes the base of a traingle, and what about the height? Well, all triangles have three distinct bases as well as three distinct heights. However, each base corresponds to a single height. You can not mix and match for the purposes of finding the area of the triangle.

Each side of the triangle constitues one of the bases. For each base, the height is defined as the distance between the highest point on the triangle and the base along a line perpendicular to the base. To perependicular lines form right angles at the point where they cross each other. If the perpendicular line does not touch the base itself, then the base is extended for the purposes of measuring the height. Examples of finding heights are shown on the chalkboard.