moomoomath logo header
lime green horizontal line
Welcome to MooMooMath
Quick Math Homework Help
Geometry Coach
geometry coach lesson plans
Alternate interior angles are....

Found inside the intersected lines. (interior)

They are also  opposite sides of the transversal.


green header moomoomath-alternate interior angles
Common Core Standard: G.CO.9  High School Math
parallel lines cut by traansversal creating alternate interior  angles
Alternate Interior angles created by a Transversal
Scroll over for the answer
two parallel lines cut by transversal
two parallel lines cut by transversal create alternate interior angles
check answer
check answer
check answer
check answer
parallel lines cut by traansversal
Other angles created by the transversal

Corresponding angles ( 1 and 5 ) ( 2 and 7) (4 and 6) (3 and 8) are angles in matching corners, and have equal angle measure.

Consecutive Interior Angles are pairs of angles inside the two lines
 Angles ( 2 and 5) and (3 and 6) are consecutive interior angles are their angle measure equals 180 degrees ( supplementary)

Adjacent Angles Angles (1 and 4) ( 2 and 3 ) (5 and 6) and (7 and 8) are adjacent because they share a common side, and as a result they are supplementary. (1 and 2) (5 and 7) (4 and 3) and (6 and 8) are also adjacent angles.


What are angles 3 and 5 in the picture above called ?
What are angles 1 and 8 called ?
What are angles 1 and 5 in the picture above called ?
What are angles 4 and 6 called ?
Your turn
If the lines cut by the transversal are non- parallel, then the alternate interior angles have no angle relationship.
The alternate interior angle theorem states:

If a transversal intersects two parallel lines, then each pair of alternate interior angles are equal.
In order to help remember the difference between interior and exterior angles, I envision a hamburger. 

The alternate interior angles are inside the bun and the alternate exterior angles are found outside the bun.
Transversal
Exterior ( outside the bun)
Interior (inside the bun)
hamburger  illustrating alternate interior angles
Alternate interior angles are created when a transversal intersects two lines. 

A transversal is a line that intersects two or more lines. The  lines do not have to be parallel.

When a transversal intersects two parallel lines it creates both alternate interior and exterior angles.



line
​Angles created on opposite sides of the transversal and inside the parallel lines are called alternate interior angles. Alternate interior angles have the same degree measure when the two lines cut by the transversal are parallel. 

If the lines cut by the transversal are non- parallel, then the alternate interior angles have no angle relationship.
non-parallel lines cut by transversal
Transversal

Alternate Interior Angles