Squares and Square Roots | IT

Question 6

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:

Solution

The dashed lines divide the large square into smaller, equal parts, which helps us compare the areas.

Step 1 — Divide the large square

Let us consider the large square. The dashed lines divide the large square into four smaller, identical squares. Each of these four smaller squares has the same area. Let the area of the large square be $A_{\text{large}}$ . Let the area of one small square (formed by dashed lines) be $A_{\text{small\_dashed}}$ .

$A_{\text{large}} = 4 \times A_{\text{small\_dashed}}$

$A_{\text{small\_dashed}} = \frac{1}{4} A_{\text{large}}$

$\boxed{\text{Area of one small dashed square} = \frac{1}{4} \times \text{Area of large square}}$

Diagram 1

Step 2 — Relate to the inner square

Now, let us look at one of these four smaller dashed squares. The solid lines forming the inner square pass through the center of the large square. Each side of the inner square is a diagonal of one of these four smaller dashed squares. This diagonal divides each small dashed square into two identical right-angled triangles. One of these triangles is part of the inner square. The other triangle is one of the four corner triangles outside the inner square. So, the area of one such triangle is half the area of one small dashed square. Let the area of one such triangle be $A_{\text{triangle}}$ .

$A_{\text{triangle}} = \frac{1}{2} \times A_{\text{small\_dashed}}$

We know from Step 1 that $A_{\text{small\_dashed}} = \frac{1}{4} A_{\text{large}}$ . Let us substitute this value into the equation for $A_{\text{triangle}}$ .

$A_{\text{triangle}} = \frac{1}{2} \times \frac{1}{4} A_{\text{large}}$

$A_{\text{triangle}} = \frac{1}{8} A_{\text{large}}$

The smaller inside square is made up of four such triangles. Let the area of the smaller inside square be $A_{\text{inner}}$ .

$A_{\text{inner}} = 4 \times A_{\text{triangle}}$

$A_{\text{inner}} = 4 \times \frac{1}{8} A_{\text{large}}$

$A_{\text{inner}} = \frac{4}{8} A_{\text{large}}$

$A_{\text{inner}} = \frac{1}{2} A_{\text{large}}$

$\boxed{\text{The smaller inside square is half the area of the larger square.}}$

More questions in IT

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

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.

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.**]

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?

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?

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:

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.

Find the hypotenuse of this isosceles right triangle.

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

Q10

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

Q11

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

Q12

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

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 $\sqrt{2}$ 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 $(5, 12, 13)$ 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 $(a, b, c)$ is non-primitive, and the integers have $f$ — greater than 1 — as a common factor, then is $\left(\frac{a}{f}, \frac{b}{f}, \frac{c}{f}\right)$ a Baudhayana triple? Check this statement for $(9, 12, 15)$ . Justify this statement.