Squares and Square Roots | IT

Question 9

What is the value of 2\sqrt{2}?

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Solution

The square root of a number is a value that, when multiplied by itself, gives the original number.

Step 1 — Understanding the nature of 2\sqrt{2}

Let xx be the value of 2\sqrt{2}. This means x×x=2x \times x = 2. Let us test some whole numbers. We know that 1×1=11 \times 1 = 1. We also know that 2×2=42 \times 2 = 4. So, the value of 2\sqrt{2} must be between 1 and 2. It is not a whole number. We will find its approximate decimal value.

Step 2 — Finding the value using the long division method

We use the long division method. We write 2 as 2.0000002.000000. We pair digits from the decimal point. We find the largest number whose square is 2\le 2. This number is 1, because 12=11^2 = 1. We write 1 as the first digit of the square root. We subtract 1 from 2.

21=12 - 1 = 1

We bring down the next pair of zeros (00). Now we have 100. We double the quotient (1), which gives 2. We place a blank digit next to 2, forming 2_2\_. We multiply 2_2\_ by the same digit. We want 2_×_1002\_ \times \_ \le 100. We find that 24×4=9624 \times 4 = 96. So, the next digit is 4. We write 4 after the decimal point in the quotient. We subtract 96 from 100.

10096=4100 - 96 = 4

We bring down the next pair of zeros (00). Now we have 400. We double the current quotient (14), ignoring the decimal point. This gives 14×2=2814 \times 2 = 28. We place a blank digit next to 28, forming 28_28\_. We multiply 28_28\_ by the same digit. We want 28_×_40028\_ \times \_ \le 400. We find that 281×1=281281 \times 1 = 281. So, the next digit is 1. We write 1 in the quotient. We subtract 281 from 400.

400281=119400 - 281 = 119

We bring down the next pair of zeros (00). Now we have 11900. We double the current quotient (141), ignoring the decimal point. This gives 141×2=282141 \times 2 = 282. We place a blank digit next to 282, forming 282_282\_. We multiply 282_282\_ by the same digit. We want 282_×_11900282\_ \times \_ \le 11900. We find that 2824×4=112962824 \times 4 = 11296. So, the next digit is 4. We write 4 in the quotient. We subtract 11296 from 11900.

1190011296=60411900 - 11296 = 604

The process continues indefinitely. So, 2\sqrt{2} is approximately 1.414.

21.414\boxed{\sqrt{2} \approx 1.414}

Diagram 1

Answer

(i) The value of 2\sqrt{2} is approximately 1.414.

More questions in IT

Q1

How can one construct a square having double the area of a given square?

Q2

Why does the new dotted square have double the area of the original square?

In many of the constructions in the Śulba-Sūtra, it is desirable to construct, where needed, what Baudhāyana calls ‘east-west’ and ‘north-south’ lines, i.e., horizontal and vertical lines that are perpendicular to each other. Can you draw some horizontal and vertical lines to see why the new square has double the area of the original square? You could draw some horizontal and vertical lines as shown on the right.

Q3

Why should the extension of the vertical and horizontal sides of the original square pass through the vertices of the dotted square?

[Hint: From the diagonal property of a square, the line that bisects an angle passes through the opposite vertex. Argue why the vertical and horizontal sides of the original square bisect the two angles of the dotted square.**]

Q4

Context: So, the new square has double the area of the original square, because the original square is made up of two small triangles, while the new square is made up of four small triangles.

Q. Moreover, all these small triangles are congruent to each other. Can you explain why?

Q5

Now suppose we are given a square, and we want to construct a square whose area is half that of the original square. How would you do it?

Q6

Why is the smaller inside square half the area of the larger square?

Again, adding some east-west and north-south lines can explain it:

Q7

Why is PQRS a square? Why is its area half that of the original paper?

Explain by connecting QS and PR, finding the different angles formed, and then using tringle congruence.

Q8

Find the hypotenuse of this isosceles right triangle.

Q9

What is the value of 2\sqrt{2}?

Q10

Is 2\sqrt{2} less than or greater than 1?

Q11

Is 2\sqrt{2} less than or greater than 2?

Q12

Can we find closer bounds for 2\sqrt{2}?

Q13

Will we ever get a number with a terminating decimal representation whose square is 2?

If there is such a terminating decimal starting with 1.414... whose square is 2, then it must have a non-zero last digit. If this is the case, then the decimal representation of its square will also have a non-zero last digit after the decimal point. For example, if 2\sqrt{2} is of the form 1.414...4, then its square will be of the form—

Q14

Use this formula to check your answers in the Figure it Out on page 39.

Q15

What if we wish to combine two squares of 'different' sizes to make a large square whose area is the sum of the two smaller squares?

Q16

Why does Baudhāyana’s method work?

Q17

Can you see why the method works in the case where the two squares are the same size? Does it agree with the method we used earlier to combine two same sized squares into a bigger square?

Q19

Explain why all the angles of this new 4-sided figure are right angles and so it is a square.

Q20

List down all the Baudhāyana triples with numbers less than or equal to 20.

Q21

Is there an unending sequence of Baudhāyana triples?

Q22

Is (30, 40, 50) a Baudhāyana triple?

Is (300, 400, 500) a Baudhāyana triple?

Q23

Context: The list of Baudhāyana triples having numbers less than or equal to 20 contains the following triples — (3, 4, 5), (6, 8, 10), (9, 12, 15), (12, 16, 20).

Q. Do you see any pattern among them?

Q24

Context: All these triples can be obtained by multiplying each term of (3, 4, 5) by a certain positive integer.

Q. Can we form a conjecture on Baudhāyana triples based on this observation?

Q25

Context: Conjecture: (3k, 4k, 5k) is a Baudhāyana triple, where k is any positive integer.

Q. Is this true?

Q26

Is (5,12,13)(5, 12, 13) a primitive Baudhayana triple? What are the other primitive Baudhayana triples with numbers less than or equal to 20?

Q27

Generate 5 scaled versions of each of these primitive triples. Are these scaled versions primitive?

Q28

If (a,b,c)(a, b, c) is non-primitive, and the integers have ff — greater than 1 — as a common factor, then is (af,bf,cf)\left(\frac{a}{f}, \frac{b}{f}, \frac{c}{f}\right) a Baudhayana triple? Check this statement for (9,12,15)(9, 12, 15). Justify this statement.

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