Rationalising The Denominator
Overview
Surds are precise, but a square root lurking in a denominator makes an expression harder to read, harder to compare and harder to simplify. Rationalising the denominator is the technique that removes every irrational part from the bottom of a fraction, leaving a clean rational number underneath.
You will learn two core moves: multiplying by the surd itself when the denominator is a single term, and multiplying by the conjugate when it contains two terms. Both rest on one elegant algebraic fact: the product of conjugate surds is always rational. Master these and you will handle every rationalisation question Edexcel can set.
Objectives
- Rationalise the denominator of expressions involving surds
Mind map
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Flashcards
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Lesson Note
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Lesson Evaluation
Congratulations on completing the lesson on Rationalising The Denominator. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.
You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.
Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.
- What is the conjugate of 3 + sqrt(5)? A) 3 + sqrt(5) B) 3 - sqrt(5) C) -3 + sqrt(5) D) -3 - sqrt(5) Answer: B
- Rationalise 1 / sqrt(2). Which is correct? A) sqrt(2) B) sqrt(2) / 4 C) sqrt(2) / 2 D) 2 / sqrt(2) Answer: C
- Which identity makes the conjugate method work? A) (a + b)^2 = a^2 + 2ab + b^2 B) (a + b)(a - b) = a^2 - b^2 C) a^2 + b^2 = (a + b)^2 D) (a - b)^2 = a^2 - 2ab + b^2 Answer: B
- What is 8 / (2 * sqrt(2)) in its simplest rationalised form? A) 2 * sqrt(2) B) 4 * sqrt(2) C) sqrt(2) D) 4 / sqrt(2) Answer: A
- Rationalise 1 / (sqrt(6) - sqrt(5)). The denominator becomes: A) 1 B) 11 C) sqrt(30) D) 6 - 5 Answer: A
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Practice Mock Questions
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