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      Checking and securing understanding of advanced angle facts

      Lesson details

      Learning outcome

      I can recognise equal corresponding angles, equal alternate angles and supplementary co-interior angles.

      Key learning points

      1. Corresponding angles are equal if they are on parallel lines and the same side of the transversal.
      2. Alternate angles are equal if they are on parallel lines and the opposite sides of the transversal.
      3. Supplementary co-interior angles sum to 180°

      Keywords

      • Transversal - A transversal is a line, line segment, or ray that intersects through two or more lines at distinct (different) points.

      • Corresponding angles - Corresponding angles are a pair of angles at different vertices on the same side of a transversal in equivalent positions.

      • Alternate angles - Alternate angles are a pair of angles both between or both outside two line segments that are on opposite sides of the transversal that cuts them.

      • Co-interior angles - Co-interior angles are on the same side of the transversal line and in between the two other lines.

      Common misconception

      Alternate angles are always equal to each other.

      Alternate angles are equal when a transversal intersects parallel lines. If the transversal intersects a pair of lines that are not parallel then the alternate angles will not be equal.

      Teacher tip

      Encourage students to reflect on the importance of vocabulary use. 'Parallel lines' is integral to the definition of co-interior, corresponding angles etc.

      Licence

      This content is © Oak National Academy Limited (2025), licensed on Open Government Licence version 3.0
      except where otherwise stated. See Oak's terms & conditions
      (Collection 2).

      Lesson video

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      Prior knowledge starter quiz

      6 Questions

      Q1.
      Two lines are if they are straight lines that are always the same (non-zero) distance apart.

      Correct Answer: parallel

      Q2.
      A __________ is a line, line segment, or ray that intersects through two or more lines at distinct (different) points.

      tangent
      transformation
      translation
      Correct answer: transversal

      Q3.
      In which image(s) is the protractor in a correct position to measure the marked angle?

      An image in a quiz
      Correct Answer: An image in a quiz
      An image in a quiz
      An image in a quiz
      Correct Answer: An image in a quiz
      An image in a quiz

      Q4.
      The size of ∠AED is 105°. Therefore the size of the acute angle ∠DEC is °.

      An image in a quiz
      Correct Answer: 75, seventy five

      Q5.
      The size of ∠AED is 105°. Therefore the size of the reflex angle ∠DEA is °.

      An image in a quiz
      Correct Answer: 255, two hundred and fifty five

      Q6.
      The size of ∠AED is 105°. Therefore the size of the obtuse angle ∠CEB is °.

      An image in a quiz
      Correct Answer: 105, one hundred and five

      6 Questions

      Q1.
      The angle that is corresponding with angle $$c$$ is angle .

      An image in a quiz
      Correct Answer: g, angle g

      Q2.
      The angle that is alternate with angle $$c$$ is angle .

      An image in a quiz
      Correct Answer: e, angle e

      Q3.
      The angle that is co-interior with angle $$c$$ is angle .

      An image in a quiz
      Correct Answer: f, angle f

      Q4.
      The angle that is vertically opposite angle $$c$$ is angle .

      An image in a quiz
      Correct Answer: a, angle a

      Q5.
      Angles $$d$$ and $$e$$ are __________.

      An image in a quiz
      alternate
      Correct answer: co-interior
      corresponding
      vertically opposite

      Q6.
      Angles $$a$$ and $$g$$ are __________.

      An image in a quiz
      Correct answer: alternate
      co-interior
      corresponding
      vertically opposite

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