Powers with Rational Exponents. Radicals
Ximena wants to put grass on a square lot of $200\ \text{m}^2$ and needs to know how long its side is. The calculator gives her $14.142135\ldots$, a number that never ends. Is there an exact way to write that side and to operate with it? Yes: with radicals. At the end of the page you come back to this lot.
From radical to fractional power
You already know that $\sqrt{a}$ is the number that, when squared, gives $a$. If we want the rules of powers to keep working, we need $\left(a^{1/2}\right)^2 = a^{1}$, and that holds if $a^{1/2}=\sqrt{a}$. With the same reasoning, $a^{1/3}=\sqrt[3]{a}$, and so on for any index.
Express the following powers with fractional exponents as radicals and calculate their exact value if it is an integer: a) $27^{\frac{1}{3}}$ b) $16^{\frac{3}{4}}$ c)…
Express the following powers with fractional exponents as radicals and calculate their exact value if it is an integer:
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a) $27^{\frac{1}{3}}$
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b) $16^{\frac{3}{4}}$
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c) $5^{\frac{2}{3}}$
Write the following radicals in the form of a power with a fractional exponent and simplify the fraction in the exponent: a) $\sqrt[6]{x^2}$ b) $\sqrt[15]{a^5}$ c)…
Write the following radicals in the form of a power with a fractional exponent and simplify the fraction in the exponent:
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a) $\sqrt[6]{x^2}$
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b) $\sqrt[15]{a^5}$
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c) $\sqrt[8]{2^6}$
Operating with fractional exponents
The properties of powers from Secondary Year 3 still hold with fractional exponents. You just add, subtract, and multiply fractions.
Calculate using the laws of fractional exponents and express the final result as a simplified radical: $$ \frac{x^{\frac{1}{2}} \times \sqrt[3]{x^2}}{x^{\frac{1}{4}}} $$
Calculate using the laws of fractional exponents and express the final result as a simplified radical:
$$ \frac{x^{\frac{1}{2}} \times \sqrt[3]{x^2}}{x^{\frac{1}{4}}} $$Find the value of $x$ that satisfies the following equation, first transforming all expressions into powers of base $2$ with rational exponents: $$ \sqrt[3]{16} \times…
Find the value of $x$ that satisfies the following equation, first transforming all expressions into powers of base $2$ with rational exponents:
$$ \sqrt[3]{16} \times 2^x = \frac{\sqrt{8}}{\sqrt[4]{2}} $$Express the final solution as an irreducible fraction.
Fully simplify the following algebraic expression, assuming that $a$ and $b$ are positive real numbers. Express the final result using radical notation, leaving no…
Fully simplify the following algebraic expression, assuming that $a$ and $b$ are positive real numbers. Express the final result using radical notation, leaving no negative or fractional exponents in the solution:
$$ \left( \frac{\sqrt[4]{a^3 \times b} \times \sqrt[3]{a \times b^2}}{\sqrt[12]{a^5 \times b^7}} \right)^{-2} $$Taking factors out of and putting factors into a radical
Let's go back to Ximena's lot: $\sqrt{200}$. Look for the largest perfect square that divides $200$. It is $100$, and $200 = 100\times 2$.
Take out all possible factors from inside the following radicals: a) $\sqrt{50}$ b) $\sqrt[3]{16}$ c) $\sqrt[4]{x^7 y^5}$
Take out all possible factors from inside the following radicals:
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a) $\sqrt{50}$
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b) $\sqrt[3]{16}$
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c) $\sqrt[4]{x^7 y^5}$
Insert the factors into the radical and simplify the resulting expression if possible: a) $3 \sqrt{2}$ b) $x^2 \sqrt[3]{x}$ c) $2a \sqrt[4]{3a^2}$, with $a \ge 0$
Insert the factors into the radical and simplify the resulting expression if possible:
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a) $3 \sqrt{2}$
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b) $x^2 \sqrt[3]{x}$
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c) $2a \sqrt[4]{3a^2}$, with $a \ge 0$
Adding and subtracting like radicals
Two radicals are like radicals if they have the same index and the same radicand. They are added like like terms in algebra: you add the coefficients and the radical stays the same. That is why it is best to first take out factors and see whether like radicals appear.
A landscape architect is designing a green space in the shape of a scalene triangle and needs to calculate its perimetre to order fencing. The plans indicate that the…
A landscape architect is designing a green space in the shape of a scalene triangle and needs to calculate its perimetre to order fencing. The plans indicate that the sides measure $\sqrt{48}$ m, $\sqrt{75}$ m and $\sqrt{12}$ m. Simplify the radicals by taking out factors and calculate the exact perimetre expressed as a single radical.
In maritime navigation, the distance $d$ (in kilometers) to the visible horizon for an observer situated at a height $h$ (in meters) above sea level is approximated by…
In maritime navigation, the distance $d$ (in kilometers) to the visible horizon for an observer situated at a height $h$ (in meters) above sea level is approximated by the formula $d = \sqrt{13h}$. Two observers are at different points on a cliff at heights of $h_1 = 52$ m and $h_2 = 117$ m respectively. Calculate the exact difference between their distances to the visible horizon, simplifying the expression $\sqrt{13 \times 117} - \sqrt{13 \times 52}$ by taking out factors.
Multiplying, dividing, and raising radicals of the same index to a power
With the same index, radicals are multiplied and divided by operating on the radicands. To raise a radical to a power, the exponent goes inside.
Calculate the following products of radicals of the same index and take out factors from the result if possible: a) $\sqrt{3} \times \sqrt{12}$ b)…
Calculate the following products of radicals of the same index and take out factors from the result if possible:
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a) $\sqrt{3} \times \sqrt{12}$
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b) $\sqrt[3]{4} \times \sqrt[3]{10}$
Calculate and simplify the result of the following divisions of radicals: a) $\frac{\sqrt{72}}{\sqrt{2}}$ b) $\frac{\sqrt[3]{40}}{\sqrt[3]{5}}$
Calculate and simplify the result of the following divisions of radicals:
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a) $\frac{\sqrt{72}}{\sqrt{2}}$
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b) $\frac{\sqrt[3]{40}}{\sqrt[3]{5}}$
Calculate the following powers of radicals, moving the exponent inside the radicand and expressing the result in the simplest form possible: a) $(\sqrt[3]{5})^6$ b)…
Calculate the following powers of radicals, moving the exponent inside the radicand and expressing the result in the simplest form possible:
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a) $(\sqrt[3]{5})^6$
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b) $(\sqrt{x^3})^4$
Common index
If the indices are different, you cannot combine the radicals under one root. You have to switch to fractional exponents and look for a common denominator: the LCM of the indices.
Express as a single radical using the root of a root rule and simplify the index if possible: a) $\sqrt{\sqrt[3]{64}}$ b) $\sqrt[4]{\sqrt{x^8}}$
Express as a single radical using the root of a root rule and simplify the index if possible:
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a) $\sqrt{\sqrt[3]{64}}$
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b) $\sqrt[4]{\sqrt{x^8}}$
For the manufacture of three electronic components, protective sheets are required whose thicknesses, measured in millimeters, are given by the expressions…
For the manufacture of three electronic components, protective sheets are required whose thicknesses, measured in millimeters, are given by the expressions $A = \sqrt[3]{5}$, $B = \sqrt[4]{7}$ and $C = \sqrt[6]{24}$. Express the radicals with a common index to order the sheet thicknesses from smallest to largest.
Perform the following operations, first expressing the radicals with a common index, and take out any possible factors from the final result: a)…
Perform the following operations, first expressing the radicals with a common index, and take out any possible factors from the final result:
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a) $\sqrt{2} \times \sqrt[3]{4} \times \sqrt[4]{8}$
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b) $\frac{\sqrt[4]{27}}{\sqrt[6]{3}}$
Root of a root and nested radicals
Simplify the following expression with nested radicals by progressively moving factors into the innermost radicals and expressing the final result as a single root: $$…
Simplify the following expression with nested radicals by progressively moving factors into the innermost radicals and expressing the final result as a single root:
$$ \sqrt{2 \sqrt[3]{2 \sqrt{2}}} $$Simplify the following expression with nested radicals, reducing it to a single common index and taking out as many factors as possible from the resulting radical: $$…
Simplify the following expression with nested radicals, reducing it to a single common index and taking out as many factors as possible from the resulting radical:
$$ \sqrt{a \times \sqrt[3]{a^2 \times b \times \sqrt[4]{b^3}}} $$Prove, using strictly the properties of powers with rational exponents, that for any positive real number $x$, the expression $\sqrt[n]{\sqrt[m]{x}}$ is equivalent to…
Prove, using strictly the properties of powers with rational exponents, that for any positive real number $x$, the expression $\sqrt[n]{\sqrt[m]{x}}$ is equivalent to $\sqrt[m]{\sqrt[n]{x}}$. Then, apply this property or conversion to powers to calculate the exact numerical value of the following sum:
$$ \sqrt[3]{\sqrt{64}} + \sqrt{\sqrt[3]{729}} $$Applications in geometry
Here radicals come from areas, volumes, and diagonals. If a square has area $A$, its side is $\sqrt{A}$. If a circle has area $A=\pi r^2$, the radius is $r=\sqrt{A/\pi}$.
A circular town square has an area of $120\pi$ m$^2$. Given that the area of a circle is given by the formula $A = \pi r^2$, calculate the exact radius of the square,…
A circular town square has an area of $120\pi$ m$^2$. Given that the area of a circle is given by the formula $A = \pi r^2$, calculate the exact radius of the square, fully simplifying the radical.
An agricultural cooperative wants to fence a square piece of land whose total area is $1250 \text{ m}^2$. Calculate the exact length of the side of the land by taking…
An agricultural cooperative wants to fence a square piece of land whose total area is $1250 \text{ m}^2$. Calculate the exact length of the side of the land by taking out factors from the radical and determine how many meters of fencing they will need in total, leaving the result in its simplest radical form.
The space diagonal of a cubic water storage tank (the straight line joining two opposite vertices passing through the center of the cube) measures exactly $\sqrt{108}$…
The space diagonal of a cubic water storage tank (the straight line joining two opposite vertices passing through the center of the cube) measures exactly $\sqrt{108}$ meters. Calculate the exact length of the edge of the cube and, from it, determine the capacity of the tank in cubic meters. Express all results simplifying the radicals.
Applications in science and finance
Many formulas have a fractional exponent: the period of a planet, the growth of a culture, or compound interest when time is not a whole number of years.
In a biology laboratory, the number of bacteria in a given culture follows the expression $N(t) = 5000 \times 8^{\frac{t}{3}}$, where $t$ is the time elapsed in hours.…
In a biology laboratory, the number of bacteria in a given culture follows the expression $N(t) = 5000 \times 8^{\frac{t}{3}}$, where $t$ is the time elapsed in hours. Express this formula using radicals and calculate the exact number of bacteria present after $2$ hours.
Kepler's third law relates the orbital period $T$ of a planet to the mean radius of its orbit $r$ using the expression $T = k^{\frac{1}{2}} \times r^{\frac{3}{2}}$. If…
Kepler's third law relates the orbital period $T$ of a planet to the mean radius of its orbit $r$ using the expression $T = k^{\frac{1}{2}} \times r^{\frac{3}{2}}$. If the constant for a fictional star system is $k = 4 \times 10^{-6}$ and a planet orbits at a mean radius of $r = 25 \times 10^4$ km, calculate the exact orbital period using the properties of powers with rational exponents and radicals.
The final amount $C_f$ obtained by investing an initial principal $C_0$ at an annual compound interest rate $r$ (expressed as a decimal) for $t$ years is given by the…
The final amount $C_f$ obtained by investing an initial principal $C_0$ at an annual compound interest rate $r$ (expressed as a decimal) for $t$ years is given by the formula $C_f = C_0 (1+r)^t$. A company invests $200\,000$ pesos at an interest rate of $21$ % per year ($r = 0.21$). Using powers with fractional exponents, calculate the exact accumulated amount after $1$ year and $4$ months (which is equivalent to $t = \frac{4}{3}$ of a year). Knowing that $1.21 = 1.1^2$, simplify the result by taking out as many factors as possible from the radical.
Summary
Go back to the beginning: the side of Ximena's lot is $\sqrt{200}=\sqrt{100\cdot2}=10\sqrt{2}$ m. It is an exact value you can keep operating with; it measures approximately $14.14$ m.