Investigating Geometry: Polygons

Henrico County Public Schools


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May 2006

Lesson 3-3: Triangle Inequalities

Interactive Applet

Video Lecture


SOL G.5: The student, given information concerning the lengths of sides and/or measures of angles, will

  1. order the sides by length, igven the angle measures;
  2. order the angles by degree measure, given the side lenghts;
  3. determine whether a traingle exists; and
  4. determine the range in which the length of the third side must lie.

These concepts will be considered in the context of real-world situations.

 Applet Directions 1 Close 
  1. To reset the screen click on your browser's REFRESH button.

  2. Once you click on the applet, use the - and + keys to re-size.

  3. Click and hold a point to move the segment.

  4. Move the segments to create triangles.
 Applet Directions 2 Close 
  1. What are the side measures of the smallest triangle you can create using the segments?

  2. What are the side measures of the largest triangle you can create using the segments?

  3. Can you create a triangle with sides of 3, 4, and 7?

  4. What is a realtionship of the 3 sides of a triangle?

  Other Web Sites web Close 
  1. Glencoe: On Line Quiz
  2. Create a Triangle given three sides
 Hands-On Activities Close 
  1. Investigate Triangle Sides

  2. Forming Triangles (PDF)
 Puzzles & Problems tangram Close 

Given a rope with knots tied at equal intervals, form a triangle with the rope such that each vertex of the triangle occurs at a knot.
Suppose the rope has 13 knots, dividing the rope into 12 sections of equal length, with a perimeter of 12 units.
Let the sides of the triangle be x, y, and z. Make a table of all values of x, y, and z that satisfy the conditions of a perimeter of 12 units and the Triangle Inequality Theorem.

12 knots