103 LearnersLast updated on July 4th, 2025
Conjugates and Rationalization
Conjugates are binomial expressions, differing only in the sign between their terms (positive or negative). Rationalization is the process of eliminating radicals or complex numbers from the denominator of a fraction. In this article, we will be looking at different aspects of conjugates and rationalization.
What is a Conjugate in Math?
In mathematics, a conjugate refers to a pair of expressions that differ only in the sign between their terms. Conjugates are used to simplify expressions, especially when dealing with radicals or complex numbers.
Rationalization Definition
Rationalization is the process of eliminating irrational numbers or complex numbers from the denominator of a fraction. This is done by multiplying both the numerator and denominator by a suitable expression that removes the radical or imaginary part from the denominator.
Conjugate of a Surd
The conjugate of a surd is a binomial expression involving irrational numbers. E.g., the conjugate of surd x + yz is x - yz and vice versa. The given table will show you the surd and the conjugate of the given surd:
| Surd | Conjugate |
| 2√5 + 3 | 2√5 - 3 |
| √7 - 3 | √7 + 3 |
| 3 - √2 | 3 + √2 |
Conjugate of a Complex Number
To write the conjugate of a complex number, simply change the sign of the imaginary part and retain the real part. For e.g., the conjugate of x + yi is x - yi. The following table will show some complex numbers and their conjugates:
| Complex Number | Conjugate |
| -2.8 - (1/4)i | -2.8 + (1/4)i |
| 3 + 5i | 3 - 5i |
| √11 - (3/√2)i | √11 + (3/√2)i |
Conjugate and Rational Factor
The product of a surd and its conjugate is rational. Students can get confused between a conjugate and rational factor. But there is a small difference that helps us determine which is which. The sum of a binomial and its rational factor isn’t always a rational number, but the sum of a binomial and its conjugate is always rational.
Rationalizing Single-Term Denominator
The steps involved in rationalizing a single-term denominator are as follows:
Step 1: Identify the radical in the denominator.
Step 2: Use the same radical to multiply both the numerator and denominator.
Step 3: Simplify the denominator.
Rationalizing Two-Term Denominator
The steps involved in rationalizing a two-term denominator are as follows:
Step 1: Identify the denominator and its conjugate.
Step 2: Now that we know the conjugate, we can use it to multiply both the numerator and the denominator.
Step 3: Apply the difference of squares formula.
Step 4: Distribute the numerator.
Step 5: Write the simplified fraction.
Step 6: Simplify further if possible.
Rationalizing Three-Term Denominator
The steps involved in rationalizing a three-term denominator are as follows:
Step 1: Group the radical terms and find a suitable conjugate.
Step 2: We can now use the conjugate and multiply both the numerator and the denominator with it.
Step 3: Expand the denominator using distributive property.
Step 4: Apply the difference of squares and remove the radical.
Step 5: Multiply again by the conjugate (only if needed) to fully eliminate radicals.
Step 6: Simplify further if possible.
Common Mistakes and How to Avoid Them in Conjugates and Rationalization
Students tend to make mistakes while understanding the concept of conjugates and rationalization. Let us see some common mistakes and how to avoid them, in conjugates and rationalization:
Mistake 1
Forgetting to Multiply the Correct Conjugate
Students should remember to always change the sign between the terms to form the conjugate. They must also remember to do the difference of squares formula.
Mistake 2
Incorrect Application of the Difference of Squares Formula
Students may incorrectly add instead of subtracting when applying the formula. Remember to subtract the square of the second term when using this formula. We can also cross-verify our answer by re-expanding the expression.
Mistake 3
Not Using the Same Conjugate to Multiply Both Numerator and Denominator
To make sure we keep the fraction equivalent and avoid errors in calculations, we must always multiply both the numerator and denominator by the same conjugate.
Mistake 4
Incorrectly Expanding the Numerator
Students must apply the distributive property properly to avoid any errors in their calculations while solving problems of conjugates and rationalization.
Mistake 5
Leaving the Answer in an Unfinished Form
Students must remember to check if all terms have a common factor. They must also remember to simplify the solution wherever possible.
Real-life Applications of Conjugates and Rationalization
Conjugates and rationalization has numerous applications across various fields. Let us explore how the conjugates and rationalization is used in different areas:
- Engineering and Physics Calculations
In physics and engineering, especially in wave mechanics and signal processing, complex numbers and their conjugates are used to simplify calculations involved in studying oscillations, vibrations and electrical circuits.
- Computer Graphics and Animation
Conjugates are important in quaternion algebra, which is used to rotate objects without distortion in animation and 3D graphics. Complex conjugates are used to produce error-free quaternion rotations.
- Quantum Mechanics and Wave Functions
In quantum physics, we use complex numbers to indicate wave functions. The product of the wave function and its conjugate is used to calculate the probability density of a quantum.
Solved Examples on Conjugates and Rationalization
Problem 1
Simplify the expression (√7 + √5) / (√7 - √5) by rationalizing the denominator.
6 + √35
Explanation
Conjugate of the denominator:
The conjugate of √7 - √5 is √7 + √5
Multiply numerator and denominator:
(√7 + √5 / √7 - √5) x (√7 + √5 / √7 + √5) = (√7 + √5)2 / (√7)2 - (5)2
Expand the numerator:
(√7 + √5)2 = √7 + 2√35 + 5 = 12 + 2√35
Simplify the denominator:
7 - 5 = 2
Divide the numerator and denominator:
12 + 2√35 / 2 = 6 + √35
Problem 2
Rationalize the denominator of 4/(√3 - 2)
4 (√3 + 2) / -1 = -4√3 - 8
Explanation
Find the conjugate:
The conjugate of √3 - 2 is √3 + 2
Multiply numerator and denominator:
(4 / √3 - 2) x (√3 + 2 / (√3 + 2) = 4(√3 + 2) / (√3)2 + (2)2
Simplify the denominator:
3 - 4 = -1
Final answer:
4(√3 + 2) / -1 = -4√3 - 8
Problem 3
Rationalize the denominator of 2 / √5 - √3
√5 + √3
Explanation
Determine the conjugate:
The conjugate of √5 - √3 is √5 + √3
Multiply the numerator and denominator:
2/ (√5 - √3) x (√5 + √3) / (√5 +√ 3) = 2 (√5 + √3) / 5 - 3
Simplify the denominator:
5 - 3 = 2
Problem 4
Rationalize the denominator of 3 / (√8 + √2)
√2 / 2
Explanation
Simplify radicals in the denominator:
√8 = 2√2
√8 + √2 = 2√2 + √2 = 3√2
Rationalize by multiplying by √2:
(1/√2) x (√2 / √2) = (√2 / 2)
Problem 5
Rationalize the denominator of 1/(√2 + √3)
√3 - √2
Explanation
Determine the conjugate:
The conjugate of √2 + √3 is √2 - √3
Multiply the numerator and denominator:
(1 / √2 - √3) x (√2 + √3 / √2 + √3) = (√2 - √3) / ((√2)2 + (√3)2)
Simplify the denominator:
2 - 3 = -1
FAQs on Conjugates and Rationalization
1.What is a conjugate?
2.Why are conjugates used in algebra?
3.What is rationalization?
4.What are alternative methods to rationalization?
5.Can conjugates be used with higher-order roots?
6.How can children in Philippines use numbers in everyday life to understand Conjugates and Rationalization?
7.What are some fun ways kids in Philippines can practice Conjugates and Rationalization with numbers?
8.What role do numbers and Conjugates and Rationalization play in helping children in Philippines develop problem-solving skills?
9.How can families in Philippines create number-rich environments to improve Conjugates and Rationalization skills?
Hiralee Lalitkumar Makwana
About the Author
Hiralee Lalitkumar Makwana has almost two years of teaching experience. She is a number ninja as she loves numbers. Her interest in numbers can be seen in the way she cracks math puzzles and hidden patterns.
Fun Fact
: She loves to read number jokes and games.
