In layman’s terms, it means “get rid of the irrational number from the bottom”. So, when we are asked to rationalise the denominator, we need to change the fraction so that the bottom number is not irrational. The most common examples of irrational numbers in GCSE maths are surds and pi. You don’t really need to know this at GCSE level, but what is helpful is to know that certain numbers are irrational. For example, 4 is the denominator of the fraction 3/4.Īn irrational number is a number that cannot be written as a fraction. The denominator of a fraction is the number on the bottom of the fraction. What does rationalising the denominator actually mean? Note that Ratio s instances inherit the deficiencies from the type parameters. But the square root of 16 would not be a surd because 16 is a square number and so its root can just be written as 4, which is an integer. Rational numbers, with numerator and denominator of some Integral type. So, an example of a surd would be the square root of 18. When you square root 18, you do not get a whole number answer (you get 4.24264068711928). Another way of checking a square number is to square root it. But 18 is not a square number because there is no integer that squares to make 18. A square number is a number that is another integer (whole number) squared.įor example, 25 is a square number because it is 5 2 and 16 is a square number because it is 4 2. Be sure to factor, if possible, after you subtract the numerators so you can identify any common factors. Simply put, a surd is a square root of a non-square number. Hence we can subtract the numerators and write the result over the common denominator. To add or subtract rational expressions with a common denominator, add or subtract the numerators and place the result over the common denominator. Please note that this topic is only examinable on the higher tier GCSE, so if you are studying foundation this blog will not be applicable to you. It will cover all types of these questions that can come up in GCSE mathematics. This blog will be a guide to rationalising the denominator of a fraction.
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