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:
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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