Triangles

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Triangles

• Matt Williams

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The Definition of a Triangle

• A figure formed by connecting three non-collinear
  points.
• A triangle has three sides and three angles. The
  sum of all the angles equals 180 degrees.
• Triangles are characterized by the length of
  their sides or the measure of their angles. There
  are six types of triangles, three in each of
  these groups.
• The triangles characterized by the length of
  their sides are Isosceles, Equilateral, and
  Scalene triangles.
• The triangles characterized by the measure of
  their angles are Acute, Right, and Obtuse
  triangles.

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Triangles Length of Sides

• An equilateral triangle is one where the length
  of all the sides are equal.
• An isosceles triangle features two sides of equal
  length.
• A scalene triangle is made of sides that are not
  equal. All the sides are different lengths.

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Triangles Measure of Angles

• Remember that the sum of the angles in any
  triangle equals 180 degrees.
• A right triangle contains an angle that equals 90
  degrees. This angle is shown with a square or box
  in that angle.
• In an acute triangle all of the angles measure
  less than 90 degrees.
• An obtuse triangle has one angle with a measure
  of larger than 90 degrees.
• An equiangular triangle has all angles with equal
  measures (must be 60 degrees), and therefore also
  must have all the lengths of its sides equal
  (meaning its an equilateral triangle as well.

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Pythagorean Theorem

• The Pythagorean Theorem is used on RIGHT
  triangles to find the length of an unknown side
  if you know the lengths of the other two sides.
• The side opposite of the right angle is called
  the Hypotenuse.
• The theorem states that a²b²c² where a and
  b are the sides of the right triangle that
  contain the right angle and c is the hypotenuse.

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Activities

• Worksheet - Identifying Triangles
• Worksheet Answers
• Pythagorean Theorem
• All pictures of triangles from
• Go Math

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Resources

• Go Math - http//www.gomath.com/htdocs/lesson/tria
  ngle_lesson1.htm
• Planet Math - http//planetmath.org/encyclopedia/T
  riangle.html
• Fact Monster - http//www.factmonster.com/ipka/A08
  76325.html
• Math - http//www.math.com/school/subject3/lesson
  s/S3U2L2GL.html