Tuesday, 27 June 2017

Geometrical Construction: Spot the Error (3)

As a group, watch the clip and try to spot as many errors as possible.
Post your observations under "Comments".


43 comments:

  1. The distance that he extended the compass' arms until was wrong as he was supposed to extend it to point B. The first arc was also redundant.

    ReplyDelete
    Replies
    1. He should also start drawing at point B.

      Delete
    2. Watch the clip on how to construct the angle bisector.
      In fact, the first step in the video was correct. It was the subsequent steps (drawing arcs from point B onwards) were incorrect.
      https://sites.google.com/a/s2017.sst.edu.sg/math/sdl-03-geometrical-construction/2-angle-bisector

      Delete
  2. He should not start drawing from point A and C but draw that the points of the first arc

    ReplyDelete
  3. He should draw the arcs starting from the arms not at point C and A

    ReplyDelete
    Replies
    1. What do you mean "starting from the arms"?
      Are you referring to "arcs" instead?

      Delete
  4. He should start drawing the last 2 arcs from the intersection points from the first arc.

    ReplyDelete
    Replies
    1. The last part of the sentence could be clearer.
      I think you are trying to say "from the points where the arcs intersects with AB and CB"?

      Delete
  5. He should extend the arms to point B from point C/A

    ReplyDelete
    Replies
    1. Watch the clip (to construct the angle bisector) again - take note of the arcs and where the pointed end of the compass are placed:
      https://sites.google.com/a/s2017.sst.edu.sg/math/sdl-03-geometrical-construction/2-angle-bisector

      Delete
  6. He should not have drawn from point A and C but from the line that he had drawn earlier.

    ReplyDelete
    Replies
    1. The first part of the sentence is correct.
      The 2nd part, are you trying to say that he should have used the intersection points of the arcs and AB and CB respectively?

      Delete
  7. He should not have made the arcs from point A and C, but instead from the intersections from point B.

    ReplyDelete
    Replies
    1. The first part of the sentence is correct.
      What do you mean by "from the intersections from B"?

      Delete
  8. He should draw the arcs from the points intersected by the first arc but he drew the arcs from point A and C.

    ReplyDelete
  9. He should not have drawn the second arc from points A and C, but from the points of the first arc.

    ReplyDelete
  10. He should draw the arcs from the points which is not from points A and C but the first marked point.

    ReplyDelete
    Replies
    1. The 2nd part of the sentence could be clearer by saying "... from the intersection points between the arcs and the AB and CB respectively"

      Delete
  11. He should have drawn from the first arc instead of a and c

    ReplyDelete
    Replies
    1. Correct. It would be clearer if we say "... drawn from the intersection points between the first arc and the intersection points with AB and CB respectively"

      Delete
  12. When drawing the second and third arc, he should place the Compass Point at the intersection of the first arc and line AB and not at point A. He should also do likewise for line BC.

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  13. After drawing the first arc, he should continue drawing the second and third arcs from the first arc.

    ReplyDelete
    Replies
    1. Correct. The 2nd part of the sentence could be clearer if we say, "... from the intersection points between the arc and BC and AB"

      Delete
  14. He should have placed his pointed end of his compass on the points where lines BC and BA intersected the arcs after drawing the first arc. From there, he should draw two arcs and then, draw the bisector through the intersection point of the two arcs and reach point B.

    ReplyDelete
  15. He should have drawn from his first arc instead of from point A and C.

    ReplyDelete
    Replies
    1. To be clearer, it should be, "from the intersection points of the first arc with AB and CB"

      Delete
  16. He should extend his compass arm all the way to point b for both sides when drawing the two arcs at both sides.

    ReplyDelete
    Replies
    1. Before extending the compass, has he placed the pointed end of the compass at the correct position before he attempted to draw the 2nd pair of arc?

      Delete
  17. For the second arc, he should place the compass at the points of the first arc.

    ReplyDelete
    Replies
    1. You are correct. He should place the pointed end of the compass at where the first arc cuts the 'arms'.

      Delete
  18. For the third and fourth arc, he should have placed his compass point on the points where lines BC and BA intersected the first arc.

    ReplyDelete
  19. He should not be drawing the arcs from points A and C but instead from the point of the arc he first constructed.

    ReplyDelete
    Replies
    1. You have described correctly what he should not have done.
      The 2nd part of the description could be clearer when describing where he should place the pointed end of the compass at - the points where the first arc cuts the 'arms' (or you can say, AB and CB).

      Delete
  20. He should not have drawn the arcs A and C but the points of the first arc

    ReplyDelete
    Replies
    1. The description needs to be more precise.
      It's more like he should not have drawn the arc by placing the pointed end of the compass at points A and C. Instead he should have place the pointed end of the compass at the points where the first arc cuts the "arms" (AB and CB) to draw the two arcs.

      Delete
  21. He should have drawn the arcs from the point of the first arc he constructed and not at points A and C.

    ReplyDelete
    Replies
    1. The first part could be clearer when you say, "the point where the first arc cuts the lines AB and CB".

      Delete

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