Properties of radicals and rationalising the denominator
A result such as $\dfrac{\sqrt2}{\sqrt3+\sqrt2}$ is not a convenient answer to keep working with, and $5\sqrt3 - 2\sqrt3$ can be reduced to a single term. This section brings together the techniques for leaving any expression with radicals in its simplest form.
Simplifying: taking out factors and reducing the index
Take out as many factors as possible from the following radicals: a) $\sqrt{72}$ b) $\sqrt[3]{250}$
Take out as many factors as possible from the following radicals:
- a) $\sqrt{72}$
- b) $\sqrt[3]{250}$
Simplify the following radicals by dividing the index and the exponent by their highest common factor: a) $\sqrt[6]{27}$ b) $\sqrt[8]{16}$
Simplify the following radicals by dividing the index and the exponent by their highest common factor:
- a) $\sqrt[6]{27}$
- b) $\sqrt[8]{16}$
Express as a single radical and simplify the result: a) $\sqrt{\sqrt[3]{64}}$ b) $\left(\sqrt[3]{\sqrt{2}}\right)^6$
Express as a single radical and simplify the result:
- a) $\sqrt{\sqrt[3]{64}}$
- b) $\left(\sqrt[3]{\sqrt{2}}\right)^6$
Adding and subtracting like radicals
Two radicals are like radicals if they have the same index and the same radicand. They can only be added or subtracted if they are like radicals, just as with like terms in algebra.
Perform the following additions and subtractions of like radicals: a) $5\sqrt{3} - 2\sqrt{3} + 4\sqrt{3}$ b) $\frac{1}{2}\sqrt{7} + \frac{3}{2}\sqrt{7} - \sqrt{7}$
Perform the following additions and subtractions of like radicals:
- a) $5\sqrt{3} - 2\sqrt{3} + 4\sqrt{3}$
- b) $\frac{1}{2}\sqrt{7} + \frac{3}{2}\sqrt{7} - \sqrt{7}$
Perform the following operation, first taking out the necessary factors so that the radicals are like terms: $3\sqrt{50} + 2\sqrt{18} - \sqrt{8}$
Perform the following operation, first taking out the necessary factors so that the radicals are like terms:
$3\sqrt{50} + 2\sqrt{18} - \sqrt{8}$
Multiplying and dividing with different indices
With the same index you operate directly on the radicands; with different indices, you first have to reduce to a common index (convert the fractions in the exponents to the same denominator).
Perform the following multiplications of radicals with the same index and take out factors if possible: a) $\sqrt{2} \cdot \sqrt{8}$ b) $\sqrt[3]{4} \cdot \sqrt[3]{10}$
Perform the following multiplications of radicals with the same index and take out factors if possible:
- a) $\sqrt{2} \cdot \sqrt{8}$
- b) $\sqrt[3]{4} \cdot \sqrt[3]{10}$
Reduce to a common index and perform the following multiplication and division of radicals: $\frac{\sqrt{2} \cdot \sqrt[3]{3}}{\sqrt[6]{6}}$
Reduce to a common index and perform the following multiplication and division of radicals:
$\frac{\sqrt{2} \cdot \sqrt[3]{3}}{\sqrt[6]{6}}$
Simplify the following expression by inserting the factors into the innermost radical and expressing it as a single root: $\sqrt{2 \cdot \sqrt[3]{2}}$
Simplify the following expression by inserting the factors into the innermost radical and expressing it as a single root:
$\sqrt{2 \cdot \sqrt[3]{2}}$
Rationalising denominators
Leaving a root in the denominator is not "wrong", but it is not the standard form: we rationalise by multiplying top and bottom by whatever is needed so that the denominator is left without roots.
Rationalise the denominator of the following fractions and simplify the result: a) $\frac{6}{\sqrt{3}}$ b) $\frac{10}{\sqrt{5}}$
Rationalise the denominator of the following fractions and simplify the result:
- a) $\frac{6}{\sqrt{3}}$
- b) $\frac{10}{\sqrt{5}}$
Rationalise the following expressions by multiplying by the conjugate of the denominator: a) $\frac{4}{\sqrt{5}-1}$ b) $\frac{2}{\sqrt{3}+1}$
Rationalise the following expressions by multiplying by the conjugate of the denominator:
- a) $\frac{4}{\sqrt{5}-1}$
- b) $\frac{2}{\sqrt{3}+1}$
Rationalise the following fractions with roots of index greater than 2: a) $\frac{10}{\sqrt[5]{8}}$ b) $\frac{3}{\sqrt[4]{27}}$
Rationalise the following fractions with roots of index greater than 2:
- a) $\frac{10}{\sqrt[5]{8}}$
- b) $\frac{3}{\sqrt[4]{27}}$
Rationalise the denominator of the following fraction and simplify as much as possible by working out the numerator: $\frac{\sqrt{6}-\sqrt{2}}{\sqrt{6}+\sqrt{2}}$
Rationalise the denominator of the following fraction and simplify as much as possible by working out the numerator:
$\frac{\sqrt{6}-\sqrt{2}}{\sqrt{6}+\sqrt{2}}$
Applications in geometry and physics
In a carpentry workshop, a rectangular board with exact dimensions of $\sqrt{12}$ dm wide and $\sqrt{27}$ dm long is going to be cut. Calculate the area and perimetre of…
In a carpentry workshop, a rectangular board with exact dimensions of $\sqrt{12}$ dm wide and $\sqrt{27}$ dm long is going to be cut. Calculate the area and perimetre of the board, expressing the results in exact form using simplified radicals.
Calculate the exact length of the main diagonal $D$ of a cube with an edge length of $a = \sqrt{5}$ cm. Remember that the diagonal of a cube is calculated as…
Calculate the exact length of the main diagonal $D$ of a cube with an edge length of $a = \sqrt{5}$ cm. Remember that the diagonal of a cube is calculated as $D = \sqrt{a^2 + a^2 + a^2}$. Express the result in the most simplified form possible.
The front wall of a cabin is in the shape of an isosceles triangle. The base of the triangle measures $\sqrt{6}$ metres and the two equal sides measure $\sqrt{15}$…
The front wall of a cabin is in the shape of an isosceles triangle. The base of the triangle measures $\sqrt{6}$ metres and the two equal sides measure $\sqrt{15}$ metres each. Calculate the exact value of the height $h$ perpendicular to the base and the total area of the front wall. Rationalise the results if roots appear in the denominator.
In physics, the speed $v$ of an object can be rearranged from its kinetic energy $E_c$ and its mass $m$ using the formula $v = \sqrt{\frac{2E_c}{m}}$. If a prototype…
In physics, the speed $v$ of an object can be rearranged from its kinetic energy $E_c$ and its mass $m$ using the formula $v = \sqrt{\frac{2E_c}{m}}$. If a prototype vehicle has a mass of $m = \sqrt{3}$ kg and its kinetic energy is $E_c = 45$ J, calculate the exact value of its speed. Rationalise and take out any possible factors from the resulting root.
Back to the beginning: Rationalising with the conjugate gives $\dfrac{\sqrt2}{\sqrt3+\sqrt2} = \dfrac{\sqrt2(\sqrt3-\sqrt2)}{(\sqrt3+\sqrt2)(\sqrt3-\sqrt2)} = \dfrac{\sqrt6-2}{3-2} = \sqrt6 - 2$, and the subtraction of like radicals gives $5\sqrt3 - 2\sqrt3 = 3\sqrt3$.