Quadrilaterals | A

Question 4

Extend one of the diagonals on both sides by 2 cm.

What quadrilateral will you get now? Justify your answer.

Question diagram 1
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Solution

We will determine the properties of the diagonals of the new shape to identify the quadrilateral.

Step 1 — Understand the original figure

The diagram shows two line segments. These segments act as the diagonals of a quadrilateral. Let us call the vertical segment DVD_V and the horizontal segment DHD_H. We can count the units between the dots. The length of DVD_V is 5 units. The length of DHD_H is 5 units. So, the diagonals are equal in length (DV=DHD_V = D_H). They intersect at the exact center. This means they bisect each other. They are also perpendicular to each other. A quadrilateral whose diagonals are equal, bisect each other, and are perpendicular is a square.

Diagram 1

Step 2 — Modify one diagonal

We extend one of the diagonals on both sides by 2 cm. Let us choose the horizontal diagonal, DHD_H. Its original length was 5 units. The new length of the horizontal diagonal, DHD_H', will be: DH=5 units+2 cm+2 cmD_H' = 5 \text{ units} + 2 \text{ cm} + 2 \text{ cm} DH=5 units+4 cmD_H' = 5 \text{ units} + 4 \text{ cm} The vertical diagonal, DVD_V, remains unchanged. Its length is still 5 units. The diagonals still intersect at the same central point. This means they still bisect each other. They are also still perpendicular to each other. Now, the length of DVD_V is 5 units and the length of DHD_H' is 5 units+4 cm5 \text{ units} + 4 \text{ cm}. Since 5 units5 units+4 cm5 \text{ units} \neq 5 \text{ units} + 4 \text{ cm}, the diagonals are no longer equal in length.

Diagram 2

Step 3 — Identify the new quadrilateral

Let us list the properties of the diagonals of the new quadrilateral. The diagonals bisect each other. The diagonals are perpendicular to each other. The diagonals are of unequal length. A quadrilateral whose diagonals bisect each other is a parallelogram. A parallelogram whose diagonals are perpendicular is a rhombus. Since the diagonals are not equal, it is not a square or a rectangle. Therefore, the new quadrilateral formed is a rhombus.

Answer

The quadrilateral you will get now is a rhombus.

Justification: The diagonals of the new quadrilateral still bisect each other and are perpendicular. However, they are no longer equal in length. A quadrilateral with diagonals that bisect each other and are perpendicular is a rhombus.

More questions in A

Q1

Are squares the only quadrilaterals that have equal sidelengths? Let us explore this question through construction.

Draw two equal sides AD and AB, that are not perpendicular to each other.

Q2

Can we complete this quadrilateral so that all its sides are of the same length?

Mark a point C whose distance from B and D is equal to AB (or AD). To do this, measure AB using a compass. Keeping this length as the radius, cut arcs from B and D.

Q3

Place two rubber bands perpendicular to each other, forming diagonals of equal length. Join the ends.

What is the quadrilateral that you get? Justify your answer.

Q4

Extend one of the diagonals on both sides by 2 cm.

What quadrilateral will you get now? Justify your answer.

Q5

Take two cardboard cutouts of an equilateral triangle of sidelength 8 cm.

  • Can you join them to get a quadrilateral?
  • What type of a quadrilateral is this? Justify your answer.
Q6

Take two cardboard cutouts of an isosceles triangle with sidelengths 8 cm, 8 cm, and 6 cm.

  • What are the different ways they can be joined to get a quadrilateral?
  • What quadrilaterals are these? Justify your answers.
Q7

Take two cardboard cutouts of a scalene triangle with sides 6 cm, 9 cm, and 12 cm.

  • What are the different ways they can be joined to get a quadrilateral?
  • Are you able to identify the different quadrilaterals that are obtained by joining the triangles? Justify your answer whenever you identify a quadrilateral.
Q8

Which Quad?

Gameplay

  1. Fold a sheet into half.
  2. Now, fold it once more into a quarter.
  3. Make a triangular crease at the corner that is at the middle of the paper.
  4. Open the sheet. What is the shape formed by the creases?
  5. How would you fold the quarter paper to get the kinds of creases shown in the following image.
  6. How would you fold the quarter paper such that a square is formed?
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