Multiple Choice Question (MCQ)

Which one of the following is an irrational number?

  1. ×

    \sqrt{9}

  2. 3\sqrt{8}

  3. ×

    -\sqrt{100}

  4. ×

    \sqrt{0.64}

Collected in the board: Rational numbers

Steven Zheng posted 4 hours ago

Answer

  1. 9 is the square of 3. Square root is the inverse operation of square, which results in an integer. \sqrt{9} = 3. So it's not an irrational number.

  2. 3\sqrt{8}=3\sqrt{2\cdot 4 }=6\sqrt{2}

    Simplifying the number gives a number with square root of a prime number. So it is an irrational number.

  3. -\sqrt{100}=-10

    100 is also a perfect square. Square root of 100 gives an integer 10

  4. \sqrt{0.64} =0.8

    Square root of a decimal which is derived from an perfect square may result in a decimal, for example, 0.8 in this case. So square root of 0.64 is a rational number.

Steven Zheng posted 4 hours ago

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