What are the roots of the equation \(x^2-81=0\)?
Answer and explanation
Correct answer: \(9\) and \(-9\)
Rewriting \(x^2-81=0\) as \(x^2=81\) gives \(x=\pm 9\). Therefore, the two roots are \(9\) and \(-9\). Option B incorrectly treats 81 as a root, although 81 is the value of \(x^2\). In exams, remember to consider both the positive and negative values when taking the square root.
Frequently asked questions
What is the correct answer to this question?
\(9\) and \(-9\)
Why is this the correct answer?
Rewriting \(x^2-81=0\) as \(x^2=81\) gives \(x=\pm 9\). Therefore, the two roots are \(9\) and \(-9\). Option B incorrectly treats 81 as a root, although 81 is the value of \(x^2\). In exams, remember to consider both the positive and negative values when taking the square root.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Quadratic Equations. Topic: Roots of a Quadratic Equation.
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