Powers and Exponents
Emma posts a video. Her cousin watches it, and every hour the number of viewers doubles. How many people have watched after 10 hours? Writing $2 \cdot 2 \cdot 2 \cdot 2 \cdot 2 \cdot 2 \cdot 2 \cdot 2 \cdot 2 \cdot 2$ is slow, and it's easy to lose count of the 2s. Powers are a short way to write repeated multiplication.
What is a power?
For example, $5 \cdot 5 \cdot 5 \cdot 5 = 5^4$. The base is $5$ and the exponent is $4$. We read it "5 to the fourth power."
Move the sliders and watch how fast powers grow.
Two exponents have special names: $a^2$ is "a squared" and $a^3$ is "a cubed."
Why is $a^0 = 1$? Look at the pattern: $2^3 = 8$, $2^2 = 4$, $2^1 = 2$. Each time the exponent drops by 1, you divide by 2. The next step down is $2^0 = 2 \div 2 = 1$.
Express the following products as a power and indicate which is the base and which is the exponent in each case: a) $5 \cdot 5 \cdot 5 \cdot 5$ b) $12 \cdot 12 \cdot 12$…
Express the following products as a power and indicate which is the base and which is the exponent in each case:
- a) $5 \cdot 5 \cdot 5 \cdot 5$
- b) $12 \cdot 12 \cdot 12$
- c) $2 \cdot 2 \cdot 2 \cdot 2 \cdot 2 \cdot 2$
- d) $10 \cdot 10 \cdot 10 \cdot 10 \cdot 10$
Calculate the value of the following basic powers: a) $3^{4}$ b) $2^{5}$ c) $7^{2}$ d) $11^{0}$ e) $1^{25}$
Calculate the value of the following basic powers:
- a) $3^{4}$
- b) $2^{5}$
- c) $7^{2}$
- d) $11^{0}$
- e) $1^{25}$
Look at the following square made up of small cells. Express the total number of cells as a power and calculate its result.
Look at the following square made up of small cells. Express the total number of cells as a power and calculate its result.
Squares, cubes, and growth
Powers show up in shapes and in things that grow. A square with 4 cells on each side has $4 \cdot 4 = 4^2 = 16$ cells.
A cube with 3 blocks on each edge holds $3 \cdot 3 \cdot 3 = 3^3 = 27$ blocks. That is where "squared" and "cubed" come from: area and volume.
Growth works the same way. If the viewers double every hour starting from 1 viewer:
| Hour | Viewers |
|---|---|
| 0 | $2^0 = 1$ |
| 1 | $2^1 = 2$ |
| 2 | $2^2 = 4$ |
| 3 | $2^3 = 8$ |
| $n$ | $2^n$ |
The exponent counts the hours. That is why the exponent is the part that changes.
A content creator publishes a video that goes viral. If every hour the number of people who have seen it triples ($3^{n}$), complete the following table expressing the…
A content creator publishes a video that goes viral. If every hour the number of people who have seen it triples ($3^{n}$), complete the following table expressing the results as a power:
| Time elapsed | People who have seen the video |
|---|---|
| At the start (Hour 0) | $3^{0} = 1$ |
| After 1 hour | $3^{1} = 3$ |
| After 2 hours | |
| After 5 hours | |
| After $n$ hours |
A video by a streamer has gone viral on a social network. During the first few hours, the number of people sharing the video triples every hour. If 3 people shared it at…
A video by a streamer has gone viral on a social network. During the first few hours, the number of people sharing the video triples every hour. If 3 people shared it at the beginning:
a) Write as a power the number of people who will have shared the video after 5 hours.
b) Calculate the value of this power to find the total number of people at that time.
Multiplying and dividing powers with the same base
Why do exponents add when you multiply? Just write out the factors and count them.
Some problems write division with a colon, $a : b$, or as a fraction $\dfrac{a}{b}$. Both mean $a \div b$.
A base with no visible exponent has exponent 1, so $10 = 10^1$. That's how you handle $10^2 \cdot 10 \cdot 10^3 = 10^{2+1+3}$.
Apply the properties of powers to write the result as a single power: a) $3^{4} \cdot 3^{2} \cdot 3^{5}$ b) $a^{3} \cdot a^{4}$ c) $10^{2} \cdot 10 \cdot 10^{3}$ d)…
Apply the properties of powers to write the result as a single power:
- a) $3^{4} \cdot 3^{2} \cdot 3^{5}$
- b) $a^{3} \cdot a^{4}$
- c) $10^{2} \cdot 10 \cdot 10^{3}$
- d) $2^{6} \cdot 2^{6}$
Reduce to a single power using the property of the quotient of powers with the same base: a) $5^{8} : 5^{3}$ b) $x^{10} : x^{7}$ c) $10^{6} : 10^{5}$ d)…
Reduce to a single power using the property of the quotient of powers with the same base:
- a) $5^{8} : 5^{3}$
- b) $x^{10} : x^{7}$
- c) $10^{6} : 10^{5}$
- d) $\dfrac{2^{9}}{2^{4}}$
Apply the properties of powers to reduce the following expressions to a single power: a) $2^5 \cdot 2^3 \cdot 2 =$ b) $(3^4)^3 : 3^7 =$ c) $\frac{5^8 \cdot 5^2}{5^7} =$
Apply the properties of powers to reduce the following expressions to a single power:
a) $2^5 \cdot 2^3 \cdot 2 =$
b) $(3^4)^3 : 3^7 =$
c) $\frac{5^8 \cdot 5^2}{5^7} =$
Power of a power, of a product, and of a quotient
What is $(4^3)^2$? It is $4^3$ used as a factor twice, so $(4^3)^2 = 4^3 \cdot 4^3 = 4^{3+3} = 4^6$. Adding $3$ two times is the same as $3 \cdot 2$.
The product rule explains the earlier surprise: $(2 \cdot 5)^3 = 2^3 \cdot 5^3$, so $2^3 \cdot 5^3 = 10^3$.
Simplify the following expressions, leaving the result as a single power: a) $(4^{3})^{2}$ b) $(10^{5})^{4}$ c) $(x^{2})^{8}$
Simplify the following expressions, leaving the result as a single power:
- a) $(4^{3})^{2}$
- b) $(10^{5})^{4}$
- c) $(x^{2})^{8}$
In a logistics warehouse, boxes are organized on cubic shelves. A storage block is made up of 4 shelves in width, 4 in length, and 4 in height. If each shelf contains 4…
In a logistics warehouse, boxes are organized on cubic shelves. A storage block is made up of 4 shelves in width, 4 in length, and 4 in height. If each shelf contains 4 boxes:
a) Express the total number of boxes as a single power.
b) If each box contains $2^3$ packs of paper, how many packs of paper are there in total in the block? Express the result as a power of base 2.
In an archaeological excavation near ancient Mesopotamia, a ceremonial structure made of cubic stone blocks has been found. The structure follows a pattern of "nested…
In an archaeological excavation near ancient Mesopotamia, a ceremonial structure made of cubic stone blocks has been found. The structure follows a pattern of "nested cubes". The first level is a cube of $2 \cdot 2 \cdot 2$ blocks. The second level surrounds the previous one forming a cube of $4 \cdot 4 \cdot 4$ blocks, and the third one of $8 \cdot 8 \cdot 8$ blocks.
- a) Express as a single power of base 2 the total number of blocks there would be on the fifth level if the edge of the cube continues to double at each step.
- b) If each block has a mass of $2^6$ pounds, express the total mass of the fifth-level structure as a single power.
Powers of 10 and expanded form
Powers of 10 are the best-behaved powers. The exponent tells you how many zeros follow the 1.
| Power | Value |
|---|---|
| $10^0$ | $1$ |
| $10^1$ | $10$ |
| $10^2$ | $100$ |
| $10^3$ | $1{,}000$ |
| $10^4$ | $10{,}000$ |
| $10^6$ | $1{,}000{,}000$ |
Every place value in our number system is a power of 10. That lets us write a number as a sum, using each digit times its place value. Some problems call this a polynomial expansion. In class it is usually called expanded form.
Write the polynomial expansion of the following numbers using powers of base $10$: a) $4\,527$ b) $30\,816$ c) $504$
Write the polynomial expansion of the following numbers using powers of base $10$:
- a) $4\,527$
- b) $30\,816$
- c) $504$
Write the polynomial expansion of the following numbers using powers of base 10: a) $45\,208$ b) $306\,750$ c) $7\,003\,040$
Write the polynomial expansion of the following numbers using powers of base 10:
a) $45\,208$
b) $306\,750$
c) $7\,003\,040$
Scientific notation
Astronomers and computer scientists work with huge numbers. Writing out $93{,}000{,}000$ is awkward, so we use powers of 10.
Some problems call this standard form. To convert a large number, put the decimal point after the first digit, and count how many places it moved. That count is the exponent.
To multiply or divide numbers in scientific notation, work with the front numbers and the powers of 10 separately.
Express the following data using standard form: a) The average distance from the Earth to the Moon is about $384\,400$ miles. b) The approximate world population is…
Express the following data using standard form:
a) The average distance from the Earth to the Moon is about $384\,400$ miles.
b) The approximate world population is $8\,000\,000\,000$ people.
c) A light year is approximately equal to $9\,461\,000\,000\,000$ miles.
The storage of a supercomputer is measured in "Exabytes". Knowing that $1 \text{ kilobyte} = 10^3 \text{ bytes}$, $1 \text{ megabyte} = 10^3 \text{ kilobytes}$,…
The storage of a supercomputer is measured in "Exabytes". Knowing that $1 \text{ kilobyte} = 10^3 \text{ bytes}$, $1 \text{ megabyte} = 10^3 \text{ kilobytes}$, $1 \text{ gigabyte} = 10^3 \text{ megabytes}$ and so on following the powers of 10 (terabyte, petabyte, exabyte):
- a) Express in scientific notation how many bytes there are in an Exabyte.
- b) If a high-definition video file takes up $2 \cdot 10^9$ bytes, how many files of this type can fit on a $4 \text{ Petabytes}$ disk? Express the result in scientific notation.
Finding an unknown exponent
If both sides of an equation are powers of the same base, then the exponents must be equal. So your goal is to get the same base on both sides, then set the exponents equal.
| $n$ | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
|---|---|---|---|---|---|---|---|---|
| $2^n$ | 2 | 4 | 8 | 16 | 32 | 64 | 128 | 256 |
| $3^n$ | 3 | 9 | 27 | 81 | 243 | 729 | 2,187 | 6,561 |
Find the value of the unknown $x$ in each of the following equalities by applying the properties of powers: a) $7^x \cdot 7^2 = 7^9$ b) $(5^3)^x = 5^{15}$ c)…
Find the value of the unknown $x$ in each of the following equalities by applying the properties of powers:
a) $7^x \cdot 7^2 = 7^9$
b) $(5^3)^x = 5^{15}$
c) $10^8 : 10^x = 10^3$
Find the value of the unknown $n$ in the following equalities, applying the rules of powers: a) $2^n \cdot 2^3 \cdot 2 = 1024$ b) $5^6 : 5^n = 125$ c)…
Find the value of the unknown $n$ in the following equalities, applying the rules of powers:
- a) $2^n \cdot 2^3 \cdot 2 = 1024$
- b) $5^6 : 5^n = 125$
- c) $(3^2)^n \cdot 9 = 3^{10}$
Rewriting with a common base
How can you tell which of $4^6$ and $8^4$ is bigger without computing them? Put both in the same base.
Notice that $10 = 2 \cdot 5$ is not a power of a single prime. When a problem mixes 10 with 2 or 5, split the 10 using the product rule: $10^n = (2 \cdot 5)^n = 2^n \cdot 5^n$.
Which of the following expressions is greater? Perform the necessary calculations to justify your answer without using a calculator. a) $2^6$ b) $4^3$ c) $8^2$ d) $64^1$…
Which of the following expressions is greater? Perform the necessary calculations to justify your answer without using a calculator.
a) $2^6$
b) $4^3$
c) $8^2$
d) $64^1$
What relationship do you find between the bases of all these powers?
Without calculating the full value of the powers, give a reasoned answer as to which of the following numbers is greater. To do this, use the transformation of the bases…
Without calculating the full value of the powers, give a reasoned answer as to which of the following numbers is greater. To do this, use the transformation of the bases to a common base:
$$ A = 8^{20} \cdot 4^{15} $$ $$ B = 16^{18} \cdot 2^5 $$A new social network has detected that the number of "shares" of a fake news story triples every hour. At 10:00 a.m., the news has already been shared $3^4$ times. a) At…
A new social network has detected that the number of "shares" of a fake news story triples every hour. At 10:00 a.m., the news has already been shared $3^4$ times.
- a) At what time will the number of shares exceed $3^{10}$ for the first time?
- b) If the server crashes when the number of shares reaches $9^7$, how many hours will have passed from 10:00 a.m. until the crash? Express all the steps using the properties of powers.
Powers in the order of operations
Powers are evaluated before multiplication and division. A square root, $\sqrt{25} = 5$ because $5^2 = 25$, is handled at the same stage as exponents. Work out the number under the radical sign first, as if it were in parentheses.
A square with $s$ tiles on each side has $s^2$ tiles in total. So if you know the total number of tiles in a square mosaic, the side length is its square root.
Calculate the value of the following combined expressions respecting the order of operations: a) $2^4 - 3^2 + \sqrt{25} \cdot 2 =$ b) $(5-2)^3 + 10^2 : (2^2 + 1) =$ c)…
Calculate the value of the following combined expressions respecting the order of operations:
a) $2^4 - 3^2 + \sqrt{25} \cdot 2 =$
b) $(5-2)^3 + 10^2 : (2^2 + 1) =$
c) $2 \cdot (3^2 - 4) + \sqrt{64} : 2^3 =$
A square mosaic made up of square tiles is to be designed. It is known that the number of tiles used is the solution to the following operation: $$ \sqrt{10^2 - 8^2}…
A square mosaic made up of square tiles is to be designed. It is known that the number of tiles used is the solution to the following operation:
$$ \sqrt{10^2 - 8^2} \cdot (3^3 - 5^2)^2 - 2^3 $$- a) How many tiles will the mosaic have in total?
- b) How many tiles will there be on each side of the square mosaic?
Calculate the value of the following combined expression, applying the properties of powers whenever possible to simplify the calculation before working it out: $$…
Calculate the value of the following combined expression, applying the properties of powers whenever possible to simplify the calculation before working it out:
$$ \frac{(2^3 \cdot 2^2)^2 \cdot 5^7 \cdot 10^3}{(5^2)^4 \cdot 2^{12}} + \sqrt{144} : 2^2 $$Powers in prime factorization: GCF and LCM
When numbers are written as products of prime powers, the greatest common factor (GCF) and the least common multiple (LCM) are easy to read off.
Why? A common factor can only use as many copies of a prime as both numbers have, so you take the smaller exponent. A common multiple needs enough copies for either number, so you take the larger one.
You can also work backward. If the GCF has $3^1$ and the LCM has $3^2$, and one of the numbers has $3^2$, then the other number must have $3^1$. One of the two exponents is the minimum and the other is the maximum.
A natural number $X$ has the following prime factorization: $X = 2^a \cdot 3^2 \cdot 5^b$. It is known that: The greatest common factor of $X$ and $180$ is…
A natural number $X$ has the following prime factorization: $X = 2^a \cdot 3^2 \cdot 5^b$.
It is known that:
-
The greatest common factor of $X$ and $180$ is $2^2 \cdot 3^2 \cdot 5^0$.
-
The least common multiple of $X$ and $180$ is $2^3 \cdot 3^2 \cdot 5^1$.
Find the values of the exponents $a$ and $b$ and write the number $X$ in decimal notation. (Fact: $180 = 2^2 \cdot 3^2 \cdot 5^1$).
Back to the start: Emma's video starts with 1 viewer and the number doubles every hour. After 10 hours, the viewers number $2^{10} = 1{,}024$.