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How Do You Classify Triangles?

Classify triangles by their angle measures and sides.

Summary

  1. The little circle after the number is the degree symbol
  2. a) is an obtuse triangle because one of its angles is obtuse (greater than 90 degrees)
  3. a) is isosceles because it has two congruent sides and angles
  4. b) is a right triangle because it has a right angle, which is shown by the box
  5. b) is scalene because all of its sides are different lengths
  6. c) is an acute triangle because all of its angles are acute (less than 90 degrees)
  7. c) is an equilateral triangle because all of its sides are equal

Notes

    1. The 'm' with an angle symbol means that we're looking at the measurement of the angle
    2. The little circle after the number is the degree symbol
    3. So this reads: The measure of angle NGP is 38 degrees
    4. Any angle less than 90 degrees is called acute
    5. Any angle greater than 90 degrees is called obtuse
    6. Since a) has an obtuse angle in it, it is an obtuse triangle
    1. The bars mean that GN, NP, and GP are sides or 'line segments'
    2. Since GN and NP are congruent (equal in length) we know that this triangle is isosceles
    3. Anytime there is a triangle with two congruent angles, we know that the triangle has two congruent sides opposite those angles
    1. The 'm' with an angle symbol means that we're looking at an angle measurement
    2. The bubble after the number means degree
    3. So, this reads: The measure of angle FRT is 22 degrees
    4. Any angle less than 90 degrees is called acute
    5. Any angle equal to 90 degrees is called a 'right angle'
    6. Since b) has a right angle in it, it is a right triangle
    7. The box in the angle means that it's a right angle
    1. The bars mean that RF, RT, and FT are sides or 'line segments'
    2. Since all three sides are different lengths, triangle b) is a scalene triangle
    1. The 'm' with an angle symbol means that we're looking at the measurement of the angle
    2. The little circle after the number is the degree symbol
    3. So this reads: The measure of angle BCS is 60 degrees
    4. Any angle less than 90 degrees is called acute
    5. Since all the angles in c) are acute, we know that c) is an acute triangle
    1. The bars mean that BC, CS and BS are sides or 'line segments'
    2. Since all three sides of triangle c) are equal, it's an equilateral triangle
    3. Equilateral triangles are always acute triangles because all of their angles always measure 60 degrees