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Last updated on September 12, 2025
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 explore different aspects of conjugates and rationalization.
In mathematics, a conjugate refers to a pair of expressions that differ only in the sign between their terms. Conjugates help simplify expressions, particularly when radicals or complex numbers are involved.
Rationalization is the process of eliminating irrational numbers or complex numbers from the denominator of a fraction. This is achieved by multiplying both the numerator and the denominator by a suitable expression. This removes the radical or imaginary part from the denominator.
The conjugate of a surd is a binomial expression involving irrational numbers. E.g., the conjugate of surd x + y√z is x - y√z 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 |
To write the conjugate of a complex number, simply change the sign of the imaginary part and retain the real part.For example, 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 |
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. While adding a binomial to its rational factor may not yield a rational number, adding a binomial to its conjugate always results in a rational number.
The steps involved in rationalizing a single-term denominator are as follows:
Step 1: Identify the radical in the denominator.
Step 2: Multiply both the numerator and denominator by the same radical.
Step 3: Simplify the 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.
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.
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:
Conjugates and rationalization have numerous applications across various fields. Let us explore how the conjugates and rationalization is used in different areas:
Simplify the expression (√7 + √5) / (√7 - √5) by rationalizing the denominator.
6 + √35
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
Rationalize the denominator of 4/(√3 - 2)
4 (√3 + 2) / -1 = -4√3 - 8
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)² - (2)² = 3 - 4 = -1
Final answer:
4(√3 + 2) / -1 = -4√3 - 8
Rationalize the denominator of 2 / √5 - √3
√5 + √3
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
Rationalize the denominator of 3 / (√8 + √2)
√2 / 2
Simplify radicals in the denominator:
√8 = 2√2
√8 + √2 = 2√2 + √2 = 3√2
Multiply numerator and denominator by √2 to rationalize:
3 / (3√2) × (√2 / √2)
= 3√2 / 6
= √2 / 2
Rationalize the denominator of 1/(√2 + √3)
√3 - √2
Determine the conjugate:
The conjugate of √2 + √3 is √2 - √3
Multiply the numerator and denominator:
(1 / (√2 + √3)) × ((√2 - √3) / (√2 - √3))
= (√2 - √3) / ((√2)2 + (√3)2)
Simplify the denominator:
(√2)² - (√3)²
= 2 - 3 = -1
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.
: She loves to read number jokes and games.