We think you are located in United States. Is this correct?

Chapter summary

Test yourself now

High marks in science are the key to your success and future plans. Test yourself and learn more on Siyavula Practice.

Sign up and test yourself

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)