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227 LearnersLast updated on December 15, 2025
Square Root of 81/4
What is the Square Root of 81/4?
The square root is the inverse of squaring a number. 81/4 is a perfect square.
The square root of 81/4 is expressed in both radical and exponential forms.
In the radical form, it is expressed as √(81/4), whereas (81/4)^(1/2) in the exponential form.
√(81/4) = 9/2, which is a rational number because it can be expressed in the form of p/q, where p and q are integers and q ≠ 0.
Finding the Square Root of 81/4
The prime factorization method is usually used for finding the square roots of numbers that can be expressed as perfect squares.
For 81/4, since it is a perfect square fraction, we can use a straightforward method to find its square root:
- Simplify the fraction
- Take the square root of the numerator and the denominator separately
Square Root of 81/4 by Simplification Method
The simplification method involves taking the square root of both the numerator and the denominator separately.
Let's see how it works for 81/4:
Step 1: Simplify the fraction 81/4
Step 2: Find the square root of the numerator (81) and the denominator (4) √81 = 9 and √4 = 2
Step 3: The square root of 81/4 is 9/2
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Square Root of 81/4 by Rationalization
Rationalization is used to eliminate any radicals in the denominator. Since 81/4 is already a simple fraction, we do not need to rationalize further.
However, we can see how rationalization would work:
Step 1: Express the square root in fractional form: √(81/4) = √81/√4
Step 2: Calculate the square roots separately: √81 = 9, √4 = 2
Step 3: The result is already rational: 9/2
Checking the Square Root of 81/4
To confirm our result, we can square the obtained square root and check if we get back the original number:
Step 1: Square (9/2) (9/2)² = 81/4
Step 2: The result confirms our square root is correct
Common Mistakes and How to Avoid Them in the Square Root of 81/4
While finding the square root, students often make mistakes such as not simplifying fractions properly or forgetting the properties of square roots.
Let's discuss some common mistakes in detail.
Mistake 1
Ignoring Fraction Simplification
Students often overlook simplifying fractions before finding the square root.
Ensure the fraction is in its simplest form before taking the square root.
Example: √(81/4) should be simplified to 9/2, not calculated separately as √81 and √4 without considering the fraction.
Mistake 2
Forgetting Both Positive and Negative Roots
A number has both positive and negative square roots.
While the principal square root is positive, students should remember that the negative root also exists.
For example: √(81/4) = ±9/2.
Mistake 3
Misapplying the Square Root to Non-Perfect Fractions
When dealing with non-perfect square fractions, students might wrongly assume a value without simplification.
Ensure proper simplification before calculating.
Example: √(50/3) needs simplification before root extraction.
Mistake 5
Errors in Rationalization
While rationalizing, students might incorrectly apply formulas.
Ensure the correct application of rationalization steps, although for √(81/4), it is not needed as the result is already rational.
Square Root of 81/4 Examples
Problem 1
Can you help Max find the area of a square box if its side length is given as √(81/4)?
The area of the square is 20.25 square units.
Explanation
The area of the square = side².
The side length is given as √(81/4).
Area of the square = (9/2) × (9/2) = 81/4 = 20.25
Therefore, the area of the square box is 20.25 square units.
Problem 2
A square-shaped garden measures 81/4 square feet; if each side is √(81/4), what is the perimeter of the garden?
18 feet
Explanation
The perimeter of a square is 4 times the side length.
Since each side is √(81/4) or 9/2, Perimeter = 4 × (9/2) = 36/2 = 18 feet
Problem 3
Calculate √(81/4) × 5.
22.5
Explanation
First, find the square root of 81/4 which is 9/2.
Then multiply 9/2 by 5: (9/2) × 5 = 45/2 = 22.5
Problem 4
What will be the square root of (64/4 + 17/4)?
The square root is 9/2.
Explanation
First, find the sum of the fractions: (64/4 + 17/4) = 81/4
Then, find the square root: √(81/4) = 9/2
Therefore, the square root of (64/4 + 17/4) is 9/2.
Problem 5
Find the perimeter of a rectangle if its length ‘l’ is √(81/4) units and the width ‘w’ is 6 units.
We find the perimeter of the rectangle as 27 units.
Explanation
Perimeter of the rectangle = 2 × (length + width)
Perimeter = 2 × (9/2 + 6) = 2 × (4.5 + 6) = 2 × 10.5 = 21 units.
FAQ on Square Root of 81/4
1.What is √(81/4) in its simplest form?
2.What are the factors of 81/4?
3.Calculate the square of 81/4.
4.Is 81/4 a perfect square?
5.Is 81/4 a rational number?
Important Glossaries for the Square Root of 81/4
- Square root: A square root is the inverse operation of squaring a number. Example: If 3² = 9, then √9 = 3.
- Rational number: A rational number can be expressed as a fraction p/q where p and q are integers and q ≠ 0.
- Perfect square: A perfect square is a number that is the square of an integer. Example: 81 is a perfect square because it is 9².
- Fraction: A fraction represents a part of a whole and is expressed as a ratio of two integers. Example: 81/4.
- Principal square root: The principal square root of a number is its non-negative square root. Example: The principal square root of 81/4 is 9/2.
Vikrant Sharma
About the Author
Vikrant is a passionate Mathematics teacher with over 5 years of teaching experience in both conventional and Vedic Maths. His student-focused approach combines clear concepts with motivation and encouragement, helping students build confidence and develo
Fun Fact
: He loves to play the quiz with kids through algebra to make kids love it.
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