Polygons and Triangles Study Guide (page 3)

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Updated on Oct 5, 2011

Right Triangles

Right triangles have a rule of their own. Using the Pythagorean theorem, we can calculate the missing side of a RIGHT triangle. a2+ b2 = c2(c refers to the hypotenuse)                                                                                            


Example: What is the perimeter of the triangle shown at the right?

  1. Since the perimeter is the sum of the lengths of the sides, we must first find the missing side. Use the Pythagorean theorem:

  2. Substitute the given sides for two of the letters. Remember: Side c is always the hypotenuse:
  3. To solve this equation, subtract 9 from both sides:

  4. Then, take the square root of both sides. (Note: Refer to Lesson 20 to learn about square roots.) Thus, the missing side has a length of 4 units.

  5. Adding the three sides yields a perimeter of 12:


Sometime today you'll be bored, and doodling is a good way to pass the time. Doodle with purpose: Draw a triangle! After you draw it, examine it closely to determine if it's an equilateral, isosceles, scalene, or right become! Practice with these shapes until you know them all by heart.

Find practice problems and solutions for these concepts at Polygons and Triangles Practice Questions.

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