Which of the following is the value of \(\sqrt{0.81}\)?
Answer and explanation
Correct answer: 0.9
The square root symbol denotes the principal (non-negative) root. Since \(0.81=\frac{81}{100}\), \(\sqrt{0.81}=\sqrt{\frac{81}{100}}=\frac{9}{10}=0.9\). Option B (−0.9) is a common trap because \((-0.9)^2=0.81\) as well, but the principal square root is positive. Options C and D are incorrect: \(0.09^2=0.0081\), and 0.81 is the original number, not its square root. Exam tip: convert decimals to fractions to simplify square-root calculations (e.g., \(0.81=81/100\)).
Frequently asked questions
What is the correct answer to this question?
0.9
Why is this the correct answer?
The square root symbol denotes the principal (non-negative) root. Since \(0.81=\frac{81}{100}\), \(\sqrt{0.81}=\sqrt{\frac{81}{100}}=\frac{9}{10}=0.9\). Option B (−0.9) is a common trap because \((-0.9)^2=0.81\) as well, but the principal square root is positive. Options C and D are incorrect: \(0.09^2=0.0081\), and 0.81 is the original number, not its square root. Exam tip: convert decimals to fractions to simplify square-root calculations (e.g., \(0.81=81/100\)).
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Polynomials. Topic: Irrational numbers and real numbers.
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