Rationalising The Denominator | Algebra | Maths | FuseSchool

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In this video we discover what rationalising the denominator is and how to do it. The denominator is the bottom part of a fraction. Rationalising the denominator is when we move a root from the bottom - the denominator - to the top (the numerator). For a surd to be in it’s simplest form, the denominator cannot be irrational. We cannot have a root in the denominator. It isn’t wrong to have a root at the bottom - it just isn’t considered the simplest form. To move a root from the denominator, we need to multiply the top and bottom both by the root. Sometimes there is more than just a root in the denominator. When this happens, we need to multiply by the WHOLE of the denominator but change the sign. So if it was root 2 plus 3 then we need to multiply both the numerator and the denominator by root 2 MINUS 3.
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