Triangles Contain 180°
In a triangle, the three interior angles always add to 180°:
A + B + C = 180°
Try it yourself (drag the points):
We can use that fact to find a missing angle in a triangle:
Example: Find the Missing Angle "C"
|Start With:||A + B + C = 180°|
|Fill in what we know:||38° + 85° + C = 180°|
|Rearrange||C = 180° - 38° - 85°|
|Calculate:||C = 57°|
This is a proof that the angles in a triangle equal 180°:
line (that touches the top of the triangle) is
running parallel to the base of the triangle.
- angles A are the same
- angles B are the same
And you can easily see that A + C + B does a complete rotation from one side of the straight line to the other, or 180°