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How to Find the Number of Degrees in a Triangle

A plane (flat) triangle is a three-sided polygon that has three angles. There are six types of triangles which are identified by characteristics of their sides or angles. For example, an equilateral triangle has sides of equal length. An isosceles triangle has two sides of equal length. A scalene triangle has sides of unequal lengths. A right triangle has one 90-degree angle. The angles of an acute triangle are all less than 90 degrees. An obtuse triangle has one angle greater than 90 degrees.

Protractor
Ruler
Calculator with trigonometric functions

Instructions

- 1
  
  A 180-degree protractor
  
  Measure the angles of the triangle using a protractor. Add the angles (in degrees). The sum is the number of degrees in the triangle. Or . . .
- 2
  
  Ruler and protractor
  
  Measure two angles and the side between them, two sides and the angle between them, two angles and a side adjacent to one of the angles or measure the length of the three sides. Enter the information of any of these four possibilities at the website listed in the Resource section and record the result of the calculation. Or . . .
- 3
  
  Calculator with trigonometric functions
  
  Remember your trigonometry and, if it is a right triangle, measure the lengths of the sides and use a calculator with trigonometric functions to find the sine (opposite side over long side) or cosine (adjacent side over long side) and thus the angle. Or . . .
- 4
  Learn this fact, if you are only interested in the total number of degrees in a triangle. The sum of the degrees in a triangle of any kind is 180 degrees.

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