Triangles can be classified by their sides and by their angles.
When classifying a triangle by its sides, you should look to see if any of the sides are the same length. If no sides are the same length, then it is a scalene triangle. If two sides are the same length, then it is an isosceles triangle. If all three sides are the same length, then it is an equilateral triangle. You can show that two sides are the same length by drawing tick marks through the middles of the sides. Sides with a corresponding number of tick marks are the same length.
Let's look at a few problems about classifying triangles.
1. Classify the triangle below by its sides and angles.
3. Is it possible for an obtuse triangle to be equilateral?
Earlier, you were asked how an exterior angle of a triangle is related to the interior angles of a triangle.
Set up an equation and solve:
1. What are the three ways to classify a triangle by its sides?
2. What are the four ways to classify a triangle by its angles?
3. Can a right triangle be equiangular? Explain.
9. Find the measure of each angle for the triangle in #8.
11. Use the angle measurements to order the sides of the triangle below from shortest to longest.
12. Use the side measurements to order the measures of the angles in the triangle below from smallest to largest.
To see the Review answers, open this PDF file and look for section 1.4.