Angles & Parallel Lines
Apply angle rules for triangles, polygons and parallel lines, and find missing angles with the reason for each step. Try “interior angle sum of a 12-sided polygon”.
Try an example:
What you can do with the Angles & Parallel Lines
Angle sums, polygons, parallel-line and triangle angle rules.
Enter your values or describe the problem in the calculator above. Review the result and the explanation before using it in homework, study or practical calculations.
Example input
e.g. interior angle sum of a 12-sided polygon
How the Angles & Parallel Lines works
- Identify the rule: angles on a line = 180°, triangle = 180°, or (n − 2) × 180° for an n-sided polygon.
- For parallel lines, spot alternate, corresponding or co-interior angles.
- Form an equation, solve it and state the reason in words.
Frequently asked questions
What is the interior angle sum of a polygon?
(n − 2) × 180°. A 12-sided polygon gives 10 × 180° = 1800°.
What are alternate angles?
Equal angles on opposite sides of a transversal between two parallel lines (a “Z” shape).
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Math Solver can make mistakes. Please double-check important steps and calculations.