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      Lesson details

      Learning outcome

      I can recognise that a pair of parallel lines traversed by a straight line produces supplementary co-interior angles.

      Key learning points

      1. Co-interior angles can be identified in an arrangement of 3 line segments.
      2. If two of the lines are parallel then these angles are supplementary.
      3. Knowledge of co-interior angles can be used to find unknown angles.
      4. Knowledge of co-interior, corresponding and alternate angles can be used to find unknown angles.

      Keywords

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

      Common misconception

      Pupils may believe that the co-interior angles are equal, like alternate and corresponding angles.

      Have pupils draw a pair of parallel lines and a transversal line themselves, identify the co-interior angles, are they equal?

      Teacher tip

      It can be helpful to show the pupils multiple diagrams with co-interior, alternate and corresponding angles identified and have the pupils decide which of the three is being shown at that point.

      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.
      The value of the angle marked $$a$$ is °.

      An image in a quiz
      Correct Answer: 128, one hundred and twenty eight

      Q2.
      The value of the angle marked $$x$$ is °.

      An image in a quiz
      Correct Answer: 53, fifty three

      Q3.
      Work out the value of $$m$$.

      An image in a quiz
      12
      Correct answer: 61
      85
      168

      Q4.
      Which pair of line segments are equal in length in this diagram?

      An image in a quiz
      Correct answer: AE
      BF
      CG
      Correct answer: IJ
      FG

      Q5.
      Alternate angles are a pair of angles both between or both outside two line segments that are on opposite sides of the that cuts them.

      Correct Answer: transversal

      Q6.
      Which of the following show a pair of equal corresponding angles?

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

      6 Questions

      Q1.
      Co-interior angles are on the side of the transversal line and in between the two other lines.

      Correct Answer: same

      Q2.
      Which of these diagrams show co-interior angles?

      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

      Q3.
      Which pairs of angles are co-interior?

      An image in a quiz
      $$a$$° and $$h$$°
      Correct answer: $$c$$° and $$f$$°
      $$b$$° and $$h$$°
      Correct answer: $$d$$° and $$e$$°
      $$c$$° and $$e$$°

      Q4.
      If the co-interior angles are in parallel lines then the angles are .

      equal
      Correct answer: supplementary
      conjugate

      Q5.
      The angle marked $$n$$° is ° as $$n$$° and 118° are supplementary co-interior angles.

      An image in a quiz
      Correct Answer: 62, sixty two, 62°

      Q6.
      Use this diagram to match pairs of supplementary co-interior angles.

      An image in a quiz
      Correct Answer:c,f

      f

      Correct Answer:d,e

      e

      Correct Answer:o,j

      j

      Correct Answer:p,i

      i

      Correct Answer:h,k

      k

      Correct Answer:a,n

      n


      To help you plan your 8 maths lesson on: Co-interior angles, download all teaching resources for free and adapt to suit your pupils' needs...