Basic Geometry
Basic Geometry
Give a reason for each deduction; use only stated or proved facts.
Basic angle facts
| Fact | Result | Reason you write |
|---|---|---|
| Angles at a point add up to \(360^\circ\). | ||
| Adjacent angles on a straight line add up to \(180^\circ\). | ||
| Vertically opposite angles are equal. |
Parallel lines
| Alternate angles are equal | Corresponding angles are equal | Interior angles add up to \(180^\circ\) |
|---|---|---|
Triangle facts
| Fact | Result | Reason you write |
|---|---|---|
| Interior angles add up to \(180^\circ\). | ||
| An exterior angle equals the sum of the two interior opposite angles. | ||
| Isosceles triangle: two equal sides face equal base angles. | ||
| Equilateral triangle: all sides equal. |
Name the relevant lines or triangle, e.g. (alternate angles, \(AB\parallel CD\)).
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