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# Test yourself now

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## 12.7 Chapter summary

• The sum of angles that are formed on a straight line is $$180^{\circ}$$.
• Vertically opposite angles are always equal.
• If lines are parallel then:
• The corresponding angles are equal. (Reason: corresp $$\angle$$s; …//… )
• The alternate angles are equal. (Reason: alt $$\angle$$s; …//… )
• The co-interior angles are supplementary. (Reason: co-int $$\angle$$s; …//… ).
• Remember that you have to state which parallel lines you are using when you give the reasons above.

### Statements and abbreviations for reasons

• Angles on a straight line add up to $$180^{\circ}$$ ($$\angle$$s on a str line)
• Vertically opposite angles are equal (vert opp $$\angle$$s)
• Angles around a point add up to $$360^{\circ}$$ ($$\angle$$s around a pt)
• Corresponding angles of parallel lines are equal (corresp $$\angle$$s ; …//… )
• Alternate angles of parallel lines are equal (alt $$\angle$$s ; …//… )
• Co-interior angles between parallel lines add up to $$180^{\circ}$$ (co-int $$\angle$$s ; …//… )
• The sum of the interior angles of a triangle add up to $$180^\circ$$ (sum of $$\angle$$s in a $$\triangle$$)
• The exterior angle of a triangle is equal to the sum of the interior opposite angles (exterior $$\angle$$ of $$\triangle$$)
• The interior angles of a quadrilateral add up to $$360^\circ$$ (sum of $$\angle$$s in a quad)