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
Understand the Question
  • The decimal expansion of any irrational number is non-terminating (never ends) and non-recurring (never repeats).
  • Since 17\sqrt{17} is given to be an irrational number, by definition, its decimal expansion must share these exact properties.

Step 1 · Deduce the Decimal Expansion of 17\sqrt{17}

By definition, any irrational number has a decimal expansion that is both non-terminating and non-recurring.Diagram 1

If a number is irrational    Its decimal expansion is non-terminatingIf a number is irrational    Its decimal expansion is non-recurringGiven that 17 is irrational\begin{aligned} \text{If a number is irrational} &\implies \text{Its decimal expansion is non-terminating} \\[0.6em] \text{If a number is irrational} &\implies \text{Its decimal expansion is non-recurring} \\[0.6em] \text{Given that } \sqrt{17} &\text{ is irrational} \end{aligned}

Therefore, the decimal expansion of 17\sqrt{17} is non-terminating and non-recurring.

Answer

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

Common Mistakes
  • Rational vs. Irrational Expansions: Rational numbers have terminating or repeating decimal expansions, whereas irrational numbers are strictly non-terminating and non-recurring.
  • Unnecessary Computation: Attempting long-division square root extraction instead of using simple logical deduction from the given premise.

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 PQRSPQRS 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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