Squares and Square Roots | IT

Question 28

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(\dfrac{a}{f}, \dfrac{b}{f}, \dfrac{c}{f}\right) a Baudhayana triple? Check this statement for (9,12,15)(9, 12, 15). Justify this statement.

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Solution
Understand the Question
  • A Baudhayana triple (Pythagorean triple) is a set of positive integers (a,b,c)(a, b, c) satisfying a2+b2=c2a^2 + b^2 = c^2.
  • A triple is non-primitive if the numbers share a common factor f>1f > 1.
  • Dividing each term by ff produces the set (af,bf,cf)\left(\dfrac{a}{f}, \dfrac{b}{f}, \dfrac{c}{f}\right). We test this statement with (9,12,15)(9, 12, 15) and prove it generally using algebra.

Step 1 · Check for the Triple (9,12,15)(9, 12, 15)

Diagram 1

Check if (9,12,15)(9, 12, 15) is a Baudhayana triple:

92+122=81+144=225\begin{aligned} 9^2 + 12^2 &= 81 + 144 \\ &= 225 \end{aligned}

152=22515^2 = 225

Since 92+122=1529^2 + 12^2 = 15^2, (9,12,15)(9, 12, 15) is a Baudhayana triple.

The common factor of 9,12,9, 12, and 1515 greater than 11 is f=3f = 3.

Dividing each term by f=3f = 3:

93=3123=4153=5\begin{aligned} \dfrac{9}{3} &= 3 \\[0.6em] \dfrac{12}{3} &= 4 \\[0.6em] \dfrac{15}{3} &= 5 \end{aligned}

Now check if the resulting triple (3,4,5)(3, 4, 5) is a Baudhayana triple:

32+42=9+16=25\begin{aligned} 3^2 + 4^2 &= 9 + 16 \\ &= 25 \end{aligned}

52=255^2 = 25

Since 32+42=523^2 + 4^2 = 5^2, (3,4,5)(3, 4, 5) is a Baudhayana triple. Thus, the statement holds true for (9,12,15)(9, 12, 15).

Step 2 · Justify the General Statement

Let (a,b,c)(a, b, c) be a non-primitive Baudhayana triple, so: a2+b2=c2a^2 + b^2 = c^2

Since f>1f > 1 is a common factor of a,b,a, b, and cc, write: a=fa,b=fb,c=fca = f \cdot a', \quad b = f \cdot b', \quad c = f \cdot c' where a,b,ca', b', c' are positive integers.

Substitute these into a2+b2=c2a^2 + b^2 = c^2: (fa)2+(fb)2=(fc)2(f \cdot a')^2 + (f \cdot b')^2 = (f \cdot c')^2

f2(a)2+f2(b)2=f2(c)2f^2 \cdot (a')^2 + f^2 \cdot (b')^2 = f^2 \cdot (c')^2

f2((a)2+(b)2)=f2(c)2f^2 \cdot ((a')^2 + (b')^2) = f^2 \cdot (c')^2

Dividing both sides by f2f^2 (since f>1    f20f > 1 \implies f^2 \ne 0): f2((a)2+(b)2)f2=f2(c)2f2\dfrac{f^2 \cdot ((a')^2 + (b')^2)}{f^2} = \dfrac{f^2 \cdot (c')^2}{f^2}

(a)2+(b)2=(c)2(a')^2 + (b')^2 = (c')^2

(af)2+(bf)2=(cf)2\left(\dfrac{a}{f}\right)^2 + \left(\dfrac{b}{f}\right)^2 = \left(\dfrac{c}{f}\right)^2

Therefore, (af,bf,cf)\left(\dfrac{a}{f}, \dfrac{b}{f}, \dfrac{c}{f}\right) satisfies the condition and is a Baudhayana triple.

Answer

Yes, (af,bf,cf)\left(\dfrac{a}{f}, \dfrac{b}{f}, \dfrac{c}{f}\right) is a Baudhayana triple.

Common Mistakes
  • Dividing by ff instead of f2f^2: When squaring each side of the equation, the scale factor becomes f2f^2. Dividing the equation by f2f^2 proves the relation.
  • Common Factor Requirement: The integer ff must be a common factor of all three terms (a,b,c)(a, b, c) to ensure that af,bf,cf\dfrac{a}{f}, \dfrac{b}{f}, \dfrac{c}{f} are all integers.

More questions in IT

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Q2

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

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Q4

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Q11

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Q12

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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 1.4141.414\dots 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 1.41441.414\dots4, then its square will be of the form—

Q14

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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)(30, 40, 50) a Baudhāyana triple?

Is (300,400,500)(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)(3, 4, 5), (6,8,10)(6, 8, 10), (9,12,15)(9, 12, 15), (12,16,20)(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)(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)(3k, 4k, 5k) is a Baudhāyana triple, where kk is any positive integer.

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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 2020?

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(\dfrac{a}{f}, \dfrac{b}{f}, \dfrac{c}{f}\right) a Baudhayana triple? Check this statement for (9,12,15)(9, 12, 15). Justify this statement.

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