Properties of Exponents
A video starts with 1 person sharing it, and the number of sharers doubles every hour. After 10 hours, writing $2 \times 2 \times 2 \times \cdots$ ten times is long and easy to mess up. Powers are a short way to write repeated multiplication, and a few simple rules make them easy to work with.
What is a power?
For example, $7^3$ is read "7 to the third power." The base is $7$ and the exponent is $3$, so $7^3 = 7 \times 7 \times 7$. Exponent $2$ is called squared and exponent $3$ is called cubed. A square of side 3 has area $3^2 = 9$.
Try different bases and exponents and watch how fast powers grow.
In an old video rental store, movies were organized on shelves. If we have an expression in the form of a power such as $7^{3}$, indicate which number acts as the base…
In an old video rental store, movies were organized on shelves. If we have an expression in the form of a power such as $7^{3}$, indicate which number acts as the base and which as the exponent. Briefly explain what operation you would have to do to calculate its value (without needing to give the final result).
A well-known social network shows users' profile photos in a square grid. If Emma's photo wall is $5$ photos wide and $5$ photos high, how many photos does she have in…
A well-known social network shows users' profile photos in a square grid. If Emma's photo wall is $5$ photos wide and $5$ photos high, how many photos does she have in total? Express the result first as a multiplication of two equal factors, then as a power, and finally calculate the total value.
Work out the following special powers mentally. Remember the rules for exponents $0$ and $1$: a) $15^{1} =$ b) $8^{0} =$ c) $1^{25} =$ d) $10^{1} =$ e) $2024^{0} =$
Work out the following special powers mentally. Remember the rules for exponents $0$ and $1$:
- a) $15^{1} =$
- b) $8^{0} =$
- c) $1^{25} =$
- d) $10^{1} =$
- e) $2024^{0} =$
Square roots of perfect squares
Squaring turns $5$ into $25$. A square root goes backward: $\sqrt{25}$ asks, "what number times itself gives $25$?" The answer is $5$, because $5^2 = 25$.
Numbers like $1, 4, 9, 16, 25, \dots$ are perfect squares. Learn the first twelve:
| $n$ | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| $n^2$ | 1 | 4 | 9 | 16 | 25 | 36 | 49 | 64 | 81 | 100 | 121 | 144 |
If a number is not a perfect square, its root lies between two whole numbers. $\sqrt{500}$ is between $22$ and $23$, because $22^2 = 484$ and $23^2 = 529$.
Calculate the following exact square roots by thinking about what number multiplied by itself gives the radicand. Look at the example: $\sqrt{25} = 5$ because…
Calculate the following exact square roots by thinking about what number multiplied by itself gives the radicand. Look at the example: $\sqrt{25} = 5$ because $5^{2} = 25$.
- a) $\sqrt{16} =$
- b) $\sqrt{49} =$
- c) $\sqrt{81} =$
- d) $\sqrt{100} =$
A school courtyard is square-shaped and has a total area of $225 m^2$. The maintenance team wants to surround it with hazard tape for a sports activity, but leaving a…
A school courtyard is square-shaped and has a total area of $225 m^2$. The maintenance team wants to surround it with hazard tape for a sports activity, but leaving a free space of $2$ feet for a door on one of the sides.
- a) How long is the side of the courtyard? (Use the square root).
- b) How many feet of tape do they need to buy?
Multiplying and dividing powers with the same base
Write the factors out and the rule shows up on its own.
Why? Multiplying counts all the factors together: $2$ threes and $4$ threes make $6$ threes. Dividing cancels factors: $5$ sevens over $2$ sevens leaves $3$ sevens.
A number with no exponent has an invisible $1$: $10 = 10^1$. So $10^2 \cdot 10 \cdot 10^3 = 10^{2+1+3} = 10^6$.
Some problems write division with a colon: $a : b$ means $a \div b$. A fraction bar means the same thing.
Apply the property of the product of powers with the same base to write the following expressions as a single power (it is not necessary to calculate the final value):…
Apply the property of the product of powers with the same base to write the following expressions as a single power (it is not necessary to calculate the final value):
- a) $3^{2} \cdot 3^{4} =$
- b) $5^{3} \cdot 5^{3} =$
- c) $a^{2} \cdot a^{5} =$
- d) $10^{2} \cdot 10 \cdot 10^{3} =$ (Hint: when a number has no exponent, it is as if it had a $1$).
Use the property of the quotient of powers with the same base to simplify these operations into a single power: a) $7^{5} : 7^{2} =$ b) $10^{8} : 10^{6} =$ c)…
Use the property of the quotient of powers with the same base to simplify these operations into a single power:
- a) $7^{5} : 7^{2} =$
- b) $10^{8} : 10^{6} =$
- c) $\frac{4^{9}}{4^{7}} =$
- d) $m^{10} : m^{9} =$
A courier company organizes its parcels in large cubic containers. If a container holds $6$ boxes in length, $6$ boxes in width and $6$ boxes in height: a) Express the…
A courier company organizes its parcels in large cubic containers. If a container holds $6$ boxes in length, $6$ boxes in width and $6$ boxes in height:
- a) Express the total number of boxes in a container as a power and calculate the result.
- b) If the company has $6^2$ identical containers stored, how many boxes do they have in total? Express the result as a single power.
Power of a power, of a product, of a quotient
Write as a single power using the power of a power property: a) $(2^{3})^{2} =$ b) $(5^{4})^{3} =$ c) $(10^{2})^{5} =$ d) $(x^{3})^{4} =$
Write as a single power using the power of a power property:
- a) $(2^{3})^{2} =$
- b) $(5^{4})^{3} =$
- c) $(10^{2})^{5} =$
- d) $(x^{3})^{4} =$
Use the properties of powers to simplify the following expression and leave it as a single power of base $2$: $$\frac{(2^4 \cdot 2^3)^2}{2^5 \cdot 2}$$ Remember to…
Use the properties of powers to simplify the following expression and leave it as a single power of base $2$:
$$\frac{(2^4 \cdot 2^3)^2}{2^5 \cdot 2}$$Remember to indicate the steps followed: first operate inside the parentheses, then apply the power of a power and, finally, divide.
Calculate the following expressions in two different ways to check that the properties of powers are met: Method A: Calculating the inside of the parentheses first and…
Calculate the following expressions in two different ways to check that the properties of powers are met:
-
Method A: Calculating the inside of the parentheses first and then the power.
-
Method B: Applying the property of the power of a product or a quotient.
- a) $(2 \cdot 5)^3$
- b) $(12 : 3)^2$
- c) $(2^2 \cdot 3)^2$
Powers of 10, growth and big numbers
Powers of $10$ are the easiest powers to write out, because the exponent tells you the number of zeros.
| Power | $10^1$ | $10^2$ | $10^3$ | $10^4$ | $10^6$ | $10^9$ |
|---|---|---|---|---|---|---|
| Number | 10 | 100 | 1,000 | 10,000 | 1,000,000 | 1,000,000,000 |
So $10^4$ is a $1$ followed by $4$ zeros, and $10^9$ is one billion. Multiplying powers of $10$ just adds zeros.
Powers also describe doubling. Look at the pattern of people sharing a video when the number doubles every hour, starting from $1$.
Doubling gets big fast, so people estimate. Since $2^{10} = 1{,}024 \approx 1{,}000 = 10^3$, you can say $2^{10} \approx 10^3$.
Writing a number as $a \times 10^n$, with $1 \le a < 10$, is called scientific notation. For example, $1{,}024 = 1.024 \times 10^3$, which is about $1 \times 10^3$. Some problems call this kind of form standard form.
In a video game, every time you pass a level, your points are multiplied by $10$. If you have passed $4$ levels and the score is written as $10^{4}$, how many points do…
In a video game, every time you pass a level, your points are multiplied by $10$. If you have passed $4$ levels and the score is written as $10^{4}$, how many points do you have in total? Write the number with all its digits and explain how many zeros you have added.
In the world of computing, storage capacities are usually expressed in powers of base $10$. An external hard drive has a capacity of $10^3$ gigabytes ($GB$). If each…
In the world of computing, storage capacities are usually expressed in powers of base $10$. An external hard drive has a capacity of $10^3$ gigabytes ($GB$). If each gigabyte contains $10^3$ megabytes ($MB$), and each megabyte has $10^6$ bytes:
- a) Express the total capacity of the hard drive in bytes using a single power of $10$.
- b) How many photos of $10^6$ bytes each would fit on the hard drive? Express the result as a power.
A TikTok video goes viral. Initially, $2$ people share it. Every hour that passes, the number of people who have shared it doubles. a) How many people will have shared…
A TikTok video goes viral. Initially, $2$ people share it. Every hour that passes, the number of people who have shared it doubles.
- a) How many people will have shared the video after $10$ hours? Express the result as a power and as a natural number.
- b) If we want to represent the total number of people in standard form after $20$ hours, what would the approximate value be if $2^{10} \approx 10^3$?
Writing everything with the same base
The product and quotient rules need the same base. Often you can make the bases match, because many numbers are powers of a smaller base.
| Base 2 | Base 3 | Base 5 | |||
|---|---|---|---|---|---|
| $4 = 2^2$ | $8 = 2^3$ | $9 = 3^2$ | $27 = 3^3$ | $25 = 5^2$ | $125 = 5^3$ |
| $16 = 2^4$ | $32 = 2^5$ | $81 = 3^4$ | $243 = 3^5$ | $10 = 2 \cdot 5$ | |
| $64 = 2^6$ | $128 = 2^7$ |
Matching bases also lets you compare big numbers. Which is larger, $4^5$ or $2^9$? Since $4^5 = (2^2)^5 = 2^{10}$, compare $2^{10}$ with $2^9$. With the same base greater than $1$, the larger exponent wins, so $4^5$ is larger. A distance of $3^8$ km compared with $27^3$ km works the same way, since $27^3 = (3^3)^3 = 3^9$.
You can also divide a power by a number written in scientific notation, like $3 \cdot 10^5$. This comes up when you divide a distance by a speed to get a time. Treat the denominator as a product: match the powers that have the same base, and leave the power of $10$ alone.
The same steps work when a problem says to leave the answer "as a power operation": divide the matching bases and keep the power of $10$ as it is.
When a fraction has different bases, simplify each base separately: $\dfrac{2^7 \cdot 5^3}{2^4 \cdot 5} = 2^{7-4} \cdot 5^{3-1} = 2^3 \cdot 5^2 = 8 \times 25 = 200$.
Adding powers needs care. You can't add exponents, but equal terms can be grouped: $2^5 + 2^5 = 2 \times 2^5 = 2^1 \cdot 2^5 = 2^6$. Check: $32 + 32 = 64 = 2^6$. ✓
Apply the properties of powers and make the necessary base transformations to express the result as a single power: $\frac{2^5 \cdot (4^2)^3 \cdot 8}{2^8 \cdot 16}$…
Apply the properties of powers and make the necessary base transformations to express the result as a single power:
$\frac{2^5 \cdot (4^2)^3 \cdot 8}{2^8 \cdot 16}$
Remember that to operate with the properties of the same base, you must first decompose the numbers $4$, $8$ and $16$ into powers of base $2$.
An astronomer observes two galaxies. Galaxy A is at a distance of $3^8 \text{ km}$ from Earth and galaxy B is at a distance of $27^3 \text{ km}$. a) Which of the two…
An astronomer observes two galaxies. Galaxy A is at a distance of $3^8 \text{ km}$ from Earth and galaxy B is at a distance of $27^3 \text{ km}$.
- a) Which of the two galaxies is further away from us? Justify your answer using powers of the same base.
- b) If light travels approximately $3 \cdot 10^5 \text{ km}$ in one second, how many seconds would it take for the light from galaxy A to reach Earth? (Leave the result expressed as a power operation).
In the world of computing, units of measurement grow in powers of base $2$. We know that $1 \text{ Kilobyte (KB)} = 2^{10} \text{ bytes}$. If a school server has a…
In the world of computing, units of measurement grow in powers of base $2$. We know that $1 \text{ Kilobyte (KB)} = 2^{10} \text{ bytes}$. If a school server has a storage capacity of $64 \text{ KB}$ and we want to expand it by installing $4$ additional memory cards, each with a capacity of $16 \text{ KB}$:
- a) Express the final total capacity of the server as a single power of base $2$.
- b) How many times greater is the final capacity compared to the initial one? (Express the result as a power).
Finding an unknown exponent
If both sides of an equation are powers of the same base, the exponents must be equal. For example, $5^x = 5^3$ means $x = 3$.
Sometimes the base is the unknown. For $x^3 = 64$, find a number that used three times as a factor makes $64$. Try $4$: $4 \times 4 \times 4 = 64$, so $x = 4$.
For the exponent $0$, remember $a^0 = 1$ only when $a \neq 0$. In $x^0 = 1$, any value of $x$ works except $x = 0$.
Doubling or tripling problems use this idea too. If a video is shared by $3$ people at level $1$, and each person shares it with $3$ new people, then level $n$ has $3^n$ sharers. To find $n$ when $3^n = 243$, list the powers: $3, 9, 27, 81, 243$. That's $3^5$, so $n = 5$.
Find the value of the letter $x$ in each of the following equalities by applying the properties of powers: a) $5^x \cdot 5^4 = 5^9$ b) $(3^2)^x = 3^6$ c)…
Find the value of the letter $x$ in each of the following equalities by applying the properties of powers:
- a) $5^x \cdot 5^4 = 5^9$
- b) $(3^2)^x = 3^6$
- c) $10^7 : 10^x = 10^3$
- d) $x^3 = 64$
- e) $x^0 = 1$ (Indicate which values $x$ could not take in this case).
A TikTok video goes viral. At first, $3$ people share it. Each of those people shares it with $3$ new people, and so on in different levels of diffusion. a) How many…
A TikTok video goes viral. At first, $3$ people share it. Each of those people shares it with $3$ new people, and so on in different levels of diffusion.
- a) How many people will have shared the video at the fifth level? Express it as a power and calculate the value.
- b) If at level $n$ it has been shared by $243$ people, what is the value of $n$?
- c) Express the product of the third level and the fourth level as a single power.
Find the value of the unknown exponent $x$ in the following equalities by applying the properties of powers: a) $3^x \cdot 9^2 = 3^7$ b) $(5^3)^x : 125 = 5^9$ c)…
Find the value of the unknown exponent $x$ in the following equalities by applying the properties of powers:
- a) $3^x \cdot 9^2 = 3^7$
- b) $(5^3)^x : 125 = 5^9$
- c) $2^4 \cdot 4^x \cdot 8 = 2^{11}$
Order of operations with powers and roots
Powers and square roots follow the usual order of operations (PEMDAS):
-
Parentheses and brackets $[\ ]$, working from the inside out. A square root also groups what's under it, so $\sqrt{4^2 + 3^2}$ means do $4^2 + 3^2$ first.
-
Exponents and roots.
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Multiplication and Division, left to right.
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Addition and Subtraction, left to right.
You can use the properties of powers whenever they make a step faster, such as $2^5 \div 2^3 = 2^2$.
Solve the following combined operations, correctly applying the order of operations and the properties of powers where possible: a)…
Solve the following combined operations, correctly applying the order of operations and the properties of powers where possible:
- a) $3^3 - \sqrt{49} + 2^2 \cdot (5 - 3)^2$
- b) $(\sqrt{100} - 2^3)^2 + 4^0 \cdot 5$
- c) $2^5 : 2^3 + \sqrt{81} \cdot 3 - 1^{15}$
Calculate the value of the following combined expression, respecting the order of operations and applying the properties of powers whenever possible:…
Calculate the value of the following combined expression, respecting the order of operations and applying the properties of powers whenever possible:
$10^2 : [5^2 \cdot (2^5 : 2^3)] + \sqrt{144} \cdot (3^2 - 2^3)$
Square roots with prime factorization
Two facts make big square roots easy:
For example, $\sqrt{16 \cdot 9} = \sqrt{16} \cdot \sqrt{9} = 4 \cdot 3 = 12$, which matches $\sqrt{144} = 12$. To take the square root of a big number, factor it into primes first, then cut each exponent in half.
If a courtyard has $N$ tiles that aren't a perfect square, such as $500$ tiles, you can still estimate how many are in a row: $\sqrt{500}$ is between $22$ and $23$.
Use prime factorization to calculate the exact square root of the following numbers in a simplified way: a) $\sqrt{2^4 \cdot 3^6 \cdot 5^2}$ b) $\sqrt{1296}$ (Hint:…
Use prime factorization to calculate the exact square root of the following numbers in a simplified way:
- a) $\sqrt{2^4 \cdot 3^6 \cdot 5^2}$
- b) $\sqrt{1296}$ (Hint: factor the number first).
- c) $\sqrt{\frac{10^4 \cdot 2^2}{25}}$
A square courtyard is paved with square tiles. The total number of tiles is the result of the expression: $N = \sqrt{4^2 + 3^2} \cdot \sqrt{25 \cdot 4 \cdot 10^2}$ a)…
A square courtyard is paved with square tiles. The total number of tiles is the result of the expression:
$N = \sqrt{4^2 + 3^2} \cdot \sqrt{25 \cdot 4 \cdot 10^2}$
- a) Calculate the value of $N$ (total number of tiles).
- b) How many tiles are there on each side of the courtyard?
- c) If each tile measures $40 \text{ in}$ on each side, what is the total area of the courtyard in square feet?
Back to the start: a video that starts with $1$ person and doubles every hour has $2^{10} = 1{,}024$ sharers after $10$ hours.