Constructions and Tilings | IT

Question 14

Construct the following figure.

Question diagram 1
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Solution

The figure is a part of a larger pattern. This larger pattern would consist of 8 identical rhombuses arranged around a central point. Each rhombus would have an angle at the center.

Let us calculate this angle. The total angle in a circle is 360 degrees. The number of rhombuses in the full pattern is 8. The angle for each rhombus is found by dividing the total angle by the number of rhombuses.

=3608= \frac{360^\circ}{8}

45\boxed{\mathbf{45^\circ}}

So, each rhombus in the pattern has an acute angle of 45 degrees. We will construct one such rhombus and then replicate it.

Step 1 — Constructing a 45-degree angle

Let us start by drawing a straight line. Mark a point A on this line. This will be the common vertex for all rhombuses. With A as the center, draw a semicircle. This semicircle cuts the line at two points. Let us call these points B and C. Now, we will construct a 90-degree angle at A. With B as the center, draw an arc above the line. With C as the center and using the same radius, draw another arc that crosses the first arc. Let this intersection point be D. Draw a ray from A through D. This ray is perpendicular to the line BC. So, the angle DAC\angle DAC is 90 degrees. Next, we will bisect this 90-degree angle to get a 45-degree angle. The semicircle drawn earlier also cuts the ray AD. Let us call this intersection point E. With C as the center, draw an arc. With E as the center and using the same radius, draw another arc that crosses the previous arc. Let this intersection point be F. Draw a ray from A through F. This ray bisects DAC\angle DAC. So, the angle FAC\angle FAC is 45 degrees. This is one of the angles we need for our rhombus.

Diagram 1

Step 2 — Constructing one rhombus

We have the angle FAC=45\angle FAC = \mathbf{45} degrees. This will be an interior angle of our rhombus. Let us choose a convenient length for the side of our rhombus. Let this length be ss. With A as the center, draw an arc of radius ss. This arc cuts the ray AC at a point. Let us call this point G. The arc also cuts the ray AF at a point. Let us call this point H. So, AG and AH are two sides of our rhombus, and their length is ss. Now, we need to find the fourth vertex of the rhombus. Let us call it I. With G as the center, draw an arc of radius ss. With H as the center, draw another arc of radius ss. These two arcs will intersect at a point. Let us call this point I. Join GI and HI using straight lines. Now, AGIH is one rhombus with all sides equal to ss and an angle of 45\mathbf{45} degrees at A.

Diagram 2

Step 3 — Replicating the rhombus to form the figure

The given figure shows 5 rhombuses arranged side by side. The first, third, and fifth rhombuses are shaded. The second and fourth are unshaded. We have constructed one rhombus AGIH. Carefully erase any extra construction lines or arcs, leaving only the rhombus AGIH. Now, we need to create 5 copies of this rhombus. We can use tracing paper to make a template of the rhombus AGIH. Place the tracing paper over your constructed rhombus and trace its outline. Cut out this traced rhombus. This is your template. Place the template on a fresh sheet of paper. Draw around it to make the first rhombus. Since the first rhombus in the figure is shaded, shade this first rhombus completely. Now, rotate your template by 45\mathbf{45} degrees around point A (the common vertex). Place the rotated template next to the first rhombus, sharing the side AH (or AG depending on rotation). Draw around the template to make the second rhombus. This rhombus should be left unshaded. Rotate the template again by 45\mathbf{45} degrees around point A. Draw the third rhombus. Shade this rhombus completely. Continue this process, rotating by 45\mathbf{45} degrees each time, and alternating between shading and leaving unshaded. Draw a total of 5 rhombuses to match the given figure. The final figure will show 5 rhombuses, with the first, third, and fifth shaded, and the second and fourth unshaded.

Diagram 3

More questions in IT

Q1

How do we find such A and B?

From X and Y, draw arcs above and below XY, with the same radii. The two points at which the arcs meet, above and below XY, give us A and B, respectively.

Use this to construct an eye.

Q2

In Fig. 6.1, join A and B with a line. Where does AB intersect XY, and what is the angle formed between them?

Q3

Will the line joining the two points at which the arcs meet, above and below XY, always be the perpendicular bisector of XY, i.e., when XY is of any length, and the arcs are drawn using a radius of any length?

Q4

Which two triangles should be congruent for AB to be the perpendicular bisector of XY (that is, O is the midpoint of XY and AB is perpendicular to XY)?

Q5

How do we get these different shapes? Try!

Q6

Will C and D lie on the perpendicular bisector AB?

Q7

Justify the following statement using the facts that we have established.

Any point that has the same distance from X and Y lies on the perpendicular bisector of XY.

Q8

Given a line segment XY, how do we draw its perpendicular bisector using only an unmarked ruler and a compass?

Q9

Can we extend the method of constructing the perpendicular bisector to construct a 90° angle at any point on a line? Draw a line and mark a point O on it. Construct a 90° angle at point O.

Q10

Find a segment of this line for which O is the midpoint.

Q11

How do we construct this figure?

Q12

What is the angle between two adjacent lines?

Q13

How do we construct a 45° angle using only a ruler and a compass?

Q14

Construct the following figure.

Q15

Draw an angle. Create a copy of this angle using only a ruler and compass.

Q16

How do we implement this idea using a ruler and a compass?

Q17

How did they make these arches?

Q18

Construct this arch shape on a piece of paper.

Let us think about the support lines this figure will need.

For symmetry, we should have AB=CDAB = CD, and BAD=CDA\angle BAD = \angle CDA. How would you construct these support lines?

Q19

Use these support lines to construct an arch. If required, adjust the radii of the arcs to make the arch look more aesthetically pleasing.

Q20

How do we construct this shape?

What supporting lines will you use to draw this arch?

Remember 'Wavy Wave' from the Grade 6 Textbook?

The supporting lines are just two line segments of equal length.

Q21

If their midpoints are marked, will you be able to construct a pointed arch?

Q22

How do we construct a regular pentagon (5-sided figure) and a regular hexagon (6-sided figure)? To begin with, try to construct a pentagon and hexagon with equal sidelengths.

Q23

Can we break a regular hexagon into smaller pieces that can be constructed?

Q24

Can six congruent equilateral triangles be placed together as in Fig. 6.12? If yes, will it result in a regular hexagon?

Q25

Consider this figure. Will the 70° angle fit into the gap? What is the gap angle AOI\angle AOI?

We have, 40+60+50+30+40+90+gap angle=36040^\circ + 60^\circ + 50^\circ + 30^\circ + 40^\circ + 90^\circ + \text{gap angle} = 360^\circ.

Use this to determine whether the 70° angle fits the gap.

Q26

In Fig. 6.12 can you explain why AOD, BOE and COF are straight lines?

Q27

Construct a regular hexagon with a sidelength 4 cm using a ruler and a compass.

Q28

Context: We can construct a regular hexagon more directly if we can construct a 120° angle using a ruler and a compass.

Q. How do we do it?

Q29

Why is CAX=60\angle\text{CAX} = 60^\circ? Is there an equilateral triangle here?

Q30

Construct a regular hexagon of sidelength 5 cm.

Q31

How will you construct 30° and 15° angles?

Q32

Construct the following 6-pointed star. Note that it has a rotational symmetry.

Q33

Are the six triangles forming the 6 points of the star — Δ\DeltaAGH, Δ\DeltaBHI, Δ\DeltaCIJ, Δ\DeltaDJK, Δ\DeltaELK, Δ\DeltaFLG — equilateral? Why?

[Hint: Find the angles.]

Q34

Can a 4×64 \times 6 grid be tiled using multiple copies of 2×12 \times 1 tiles? We are allowed to rotate a 2×12 \times 1 tile and use it.

Q35

Can a 4×74 \times 7 grid be tiled using 2×12 \times 1 tiles?

Q36

What about a 5×75 \times 7 grid?

Complete the justification.

Q38

Is an m×nm \times n grid tileable with 2×12 \times 1 tiles, if both mm and nn are even? If yes, come up with a general strategy to tile it.

Q39

Is an m×nm \times n grid tileable with 2×12 \times 1 tiles, if one of mm and nn is even and the other is odd? If yes, come up with a general strategy to tile it.

Q40

Is an m×nm \times n grid tileable with 2×12 \times 1 tiles, if both mm and nn are odd? Give reasons.

Q41

Here is a 5×35 \times 3 grid, with a unit square removed. Now, it has an even number of unit squares. Is it tileable with 2×12 \times 1 tiles?

Q42

Is the following region tileable with 2×12 \times 1 tiles?

Q43

Context: We are considering whether a given region can be tiled using 2×12 \times 1 tiles.

Q. What about this one?

Q44

Were you able to tile this? How can we be sure that this is not tileable? Can you find another unit square that, when removed from a 5×35 \times 3 grid, makes it non-tileable?

Q45

If the plain grid is tileable, is the black-and-white-grid tileable?

Q46

If the black-and-white grid is tileable, is the plain grid tileable?

Q47

Use this idea to find another unit square that, when removed from a 5 × 3 grid, makes it non-tileable?

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