Appendix 1: Proofs in Mathematics | A1.2

Question 7

Given that p\sqrt{p} is irrational for all primes pp and also suppose that 3721 is a prime. Can you conclude that 3721\sqrt{3721} is an irrational number? Is your conclusion correct? Why or why not?

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Solution

We need to check if the number 3721 is actually a prime number.

Step 1 — Check the number 3721

Let's find the square root of 3721. We can try numbers close to its square root. We know that 60×6060 \times 60 is 3600. Let's try multiplying 61 by 61.

61×6161 \times 61 =3721= 3721

3721=61\boxed{\sqrt{3721} = 61}

So, 3721\sqrt{3721} is 61. This means 3721 is a perfect square. A perfect square greater than 1 is not a prime number. So, 3721 is not a prime number. It is a composite number.

Step 2 — Answer the questions

The problem gives us two statements. First, p\sqrt{p} is irrational for all primes pp. Second, it asks us to suppose 3721 is a prime. Based on these two statements, we can make a conclusion.

Answer

(i) Yes, we can conclude that 3721\sqrt{3721} is an irrational number. (ii) No, our conclusion is not correct. (iii) The premise that 3721 is a prime number is false. We found that 3721\sqrt{3721} is 61. So, 3721 is 61 multiplied by 61. This means 3721 is a composite number. Since 3721 is not prime, the given condition does not apply. 3721\sqrt{3721} is 61, which is a rational number.

More questions in A1.2

Q1

Given that all women are mortal, and suppose that A is a woman, what can we conclude about A?

Q2

Given that the product of two rational numbers is rational, and suppose aa and bb are rationals, what can you conclude about abab?

Q3

Given that the decimal expansion of irrational numbers is non-terminating, non-recurring, and 17\sqrt{17} is irrational, what can we conclude about the decimal expansion of 17\sqrt{17}?

Q4

Given that y=x2+6y = x^2 + 6 and x=1x = -1, what can we conclude about the value of yy?

Q5

Given that ABCD is a parallelogram and B=80\angle B = 80^\circ. What can you conclude about the other angles of the parallelogram?

Q6

Given that PQRS is a cyclic quadrilateral and also its diagonals bisect each other. What can you conclude about the quadrilateral?

Q7

Given that p\sqrt{p} is irrational for all primes pp and also suppose that 3721 is a prime. Can you conclude that 3721\sqrt{3721} is an irrational number? Is your conclusion correct? Why or why not?

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