Due to the fact that one outside angle of a triangle is equal to the sum of its other two angles, all of its angles add up to 180 degrees.
In other words, the third angle must be added to the other two angles in the triangle (the ones that add up to generate the outer angle) to form a 180-degree angle.
How do you determine if a triangle's angles are 180 degrees?
How Can I Determine a 180 Degree Angle?
Create a straight line to represent the angle's arm.
At one end of the line, place a dot.
Now position the protractor's center above the dot or vertex and line up the protractor's baseline with the angle's arm.
