Irrational Number Identification

XAT 2020 · Quantitative Ability & Data Interpretation · Easy · Quantitative Aptitude

When expressed in a decimal form, which of the following numbers will be non-terminating as well as non-repeating?

  1. A.

    (π2)[(1π)+1]−π2(\frac{\pi}{2}) [(\frac{1}{\pi}) + 1] - \frac{\pi}{2}

  2. B.

    \sin^2 1^\circ + \sin^2 2^\circ + .... + \sin^2 89^\circ

  3. C.

    \sqrt{2} (3\sqrt{2} - \frac{4}{\sqrt{2}}) + \sqrt{3}

  4. D.

    \frac{\sqrt[3]{729}}{3} + \frac{22}{7}

  5. E.

    (4 - \pi)[1 + (\frac{\pi}{4}) + (\frac{\pi}{4})^2 + (\frac{\pi}{4})^3 + ... \text{ (infinite terms)}]

Answer

C

Explanation

A non-terminating and non-repeating decimal represents an irrational number. Option A: π2(1π+1)−π2=12+π2−π2=12\frac{\pi}{2}(\frac{1}{\pi} + 1) - \frac{\pi}{2} = \frac{1}{2} + \frac{\pi}{2} - \frac{\pi}{2} = \frac{1}{2} (Rational). Option B: sin⁡21∘+⋯+sin⁡289∘=44.5\sin^2 1^\circ + \dots + \sin^2 89^\circ = 44.5 (Rational). Option C: 2(32−22)+3=2+3\sqrt{2}(3\sqrt{2} - 2\sqrt{2}) + \sqrt{3} = 2 + \sqrt{3} (Irrational). Option D: 93+227=3+227=437\frac{9}{3} + \frac{22}{7} = 3 + \frac{22}{7} = \frac{43}{7} (Rational). Option E: Infinite GP sum 11−π/4=44−π\frac{1}{1 - \pi/4} = \frac{4}{4-\pi}, so (4−π)×44−π=4(4 - \pi) \times \frac{4}{4-\pi} = 4 (Rational). Hence C is irrational.

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