# Consecutive Interior Angles in Parallel Lines

How to solve consecutive interior angles in parallel lines problems: definition, theorem, example, and its solution.

## Definition

By two lines and a transversal,

2 pairs of consecutive interior angles are formed.

(plain blue-purple angles, dotted blue-purple angles)

## Theorem

If a transversal passes through parallel lines,

then a pair of consecutive interior angles is supplementary.

m∠(purple) + m∠(blue) = 180

## Example

These two horizontal lines are parallel.

So the given consecutive interior angles are supplementary.

So (5*x* + 60) + (70) = 180.