Appendix 1: Proofs in Mathematics | A1.2

Question 3

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}?

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Solution

We will use the definition of irrational numbers to describe 17\sqrt{17}.

Step 1 — Recall definitions

We know what an irrational number is. Its decimal expansion is special. It is non-terminating. This means it never ends. It is also non-recurring. This means no digits repeat in a pattern.

We are given that 17\sqrt{17} is irrational. This is a key piece of information.

Diagram 1

Step 2 — Conclude about 17\sqrt{17}

Let's combine these facts. We know 17\sqrt{17} is an irrational number. We also know irrational numbers have specific properties. Their decimal expansions are non-terminating. Their decimal expansions are non-recurring. Therefore, 17\sqrt{17} must have these properties.

If a number is irrational    Its decimal expansion is non-terminating\text{If a number is irrational} \implies \text{Its decimal expansion is non-terminating} If a number is irrational    Its decimal expansion is non-recurring\text{If a number is irrational} \implies \text{Its decimal expansion is non-recurring} Given that 17 is irrational\text{Given that } \sqrt{17} \text{ is irrational}

The decimal expansion of 17 is non-terminating and non-recurring.\boxed{\text{The decimal expansion of } \sqrt{17} \text{ is non-terminating and non-recurring.}}

Answer

(i) The decimal expansion of 17\sqrt{17} is non-terminating. (ii) The decimal expansion of 17\sqrt{17} is non-recurring.

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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