Angles in parallel lines
When a line crosses two parallel lines, matching angles are equal. Alternate angles form a Z shape and are equal. Co-interior angles form a C shape and add to 180 degrees.
Last updated
Analogy
Like railway tracks crossed by a road: the same angle repeats at each crossing.
Example
Alternate angle = 62, so the other = 62Co-interior angle = 62The partner = 180 - 62 = 118
In practice
Road designers and carpenters use these rules to keep lines truly parallel.
Practice
Flashcards
- Name the angle pair that forms a Z shape in parallel lines.Alternate angles. They are equal.
Questions people ask
How do you spot alternate angles?
Look for a Z shape (or an S shape) made by the crossing line and the two parallel lines. The angles tucked inside the corners of the Z are alternate angles, and they are equal. Always check the lines are parallel, usually shown by arrows.
What is the difference between corresponding and co-interior angles?
Corresponding angles sit in the same position at each crossing, like an F shape, and are equal. Co-interior angles sit between the parallel lines on the same side, like a C shape, and add up to 180 degrees instead of being equal.