Playing with Constructions | A

Question 8

How will you record your observations? First, identify the parameters that need to be tracked. They are the sides of the rectangle and the 8 angles formed by the two diagonals. Are there any other measurements that you would want to keep track of?

Question diagram 1
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Solution

We will list all parts of the rectangle that we need to measure.

Step 1 — Sides of the Rectangle

We will name the four corners A, B, C, D.

We will measure the length of each side.

The four sides are AB, BC, CD, and DA.

Diagram 1

Step 2 — Diagonals of the Rectangle

We will draw two lines connecting opposite corners.

These lines are called diagonals.

The two diagonals are AC and BD.

We will measure the length of each diagonal.

Diagram 2

Step 3 — Angles Formed by Diagonals

The two diagonals cross each other at a point.

Let us call this point O.

They form 4 angles at this crossing point.

These angles are AOB,BOC,COD\angle AOB, \angle BOC, \angle COD, and DOA\angle DOA.

Each diagonal makes angles with the sides.

Diagonal AC makes angle DAC\angle DAC with side AD.

It also makes angle BAC\angle BAC with side AB.

Diagonal BD makes angle ABD\angle ABD with side AB.

It also makes angle CBD\angle CBD with side BC.

We will measure these 8 angles.

Diagram 3

Step 4 — Other Measurements

We can find the distance around the rectangle.

This is called the perimeter.

We can also find the space inside the rectangle.

This is called the area.

We will measure the perimeter and the area.

Answer

(i) The parameters to track are: The lengths of the four sides (AB, BC, CD, DA). The lengths of the two diagonals (AC, BD). The 8 angles formed by the diagonals: AOB,BOC,COD,DOA,DAC,BAC,ABD,CBD\angle AOB, \angle BOC, \angle COD, \angle DOA, \angle DAC, \angle BAC, \angle ABD, \angle CBD. (ii) Other measurements to track are the perimeter and the area of the rectangle.

More questions in A

Q1

Observe the following figures and try drawing them freehand.

Q2

Mark a point ‘P’ in your notebook. Then, mark as many points as possible, in different directions, that are 4 cm away from P.

Think: Imagine marking all the points of 4 cm distance from the point P. How would they look?

Try to draw it and verify if it is correct by taking some points on the curve and checking if their distances from P are indeed 4 cm. Explore, if you have not already done so, and see if a compass can be used for this purpose.

You can start by marking a few points of distance 4 cm from P using the compass. How can this be done?

Q3

Having explored the use of a compass, go ahead and recreate the images in Fig. 8.1. Can you make the figures look as good as the figures shown there? Try again if you want to!

Also, has the use of instruments made the construction easier?

Q4

Construct

1. A Person

How will you draw this?

Q5

2. Wavy Wave

Construct this.

Q6

Make other artwork of your choice with a ruler and a compass.

Q7

Explore

How should the rectangle be constructed so that the diagonal divides the opposite angles into equal parts?

Q8

How will you record your observations? First, identify the parameters that need to be tracked. They are the sides of the rectangle and the 8 angles formed by the two diagonals. Are there any other measurements that you would want to keep track of?

Q9

In your experimentation, did you consider the case when all four sides of the rectangle are equal? That is, did you consider the case of a square? See what happens in this special case!

Q10

Math Talk

What general laws did you observe with respect to the angles and sides? Try to frame and discuss them with your classmates.

How can one be sure if the laws that you have observed will always be true?

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