## alternate exterior angles theorem

### The alternate exterior angles theorem is a geometric concept that deals with the relationship between alternate exterior angles formed when a pair of parallel lines is intersected by a transversal line

The alternate exterior angles theorem is a geometric concept that deals with the relationship between alternate exterior angles formed when a pair of parallel lines is intersected by a transversal line.

When two parallel lines are intersected by a transversal line, four pairs of angles are formed. Alternate exterior angles are the pairs of angles that lie on opposite sides of the transversal and outside the two parallel lines. These angles are not adjacent (meaning they do not share a common vertex or side).

The alternate exterior angles theorem states that if two parallel lines are intersected by a transversal, then the alternate exterior angles are congruent (i.e., they have the same measure).

In other words, if we have two parallel lines (l₁ and l₂) intersected by a transversal (t), and we have alternate exterior angles A and B, then angle A is congruent to angle B. Mathematically, we represent this as:

m∠A = m∠B, where “m” represents the measure of the angle.

This theorem is a fundamental property of parallel lines and can be used to solve various geometric problems involving parallel lines and transversals. It allows us to determine the measures of unknown angles by using congruent angles as a reference.

For example, if we know the measure of one alternate exterior angle, we can immediately conclude that the angle directly opposite to it (the other alternate exterior angle) has the same measure. This theorem also enables us to prove parallelism based on angle relationships.

Understanding and applying the alternate exterior angles theorem is crucial for studying and solving problems in geometry involving parallel lines and transversals.

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