The Exterior Angle Theorem is a rule that helps us figure out angles in triangles. It says that if you have an exterior angle, it equals the sum of the two opposite interior angles.

Here’s How to Use It:

1. Find the Exterior Angle: Look for an exterior angle. This happens when you extend one side of the triangle.

2. Label the Angles: Let’s call the exterior angle $E$, and the two opposite interior angles $A$ and $B$.

The Simple Formula:

$E = A + B$

Example:

Imagine that angle $E$ is $100^\circ$, and angle $A$ is $40^\circ$. To find angle $B$, you can do the math like this:

$100^\circ = 40^\circ + B$

Now, solve for $B$:

$B = 100^\circ - 40^\circ = 60^\circ$

Using this theorem makes it easy to find unknown angles in triangle problems!