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Math 8 · Mathematics
Powers and roots · Powers

Properties of Exponents

Before you start, make sure you know: Powers (Math 7)
Before you start, make sure you know: Prime factorization (Math 7)

Fold a sheet of paper in half 42 times and the stack would reach the Moon. It sounds impossible, but every fold doubles the thickness, and $2^{42}$ is more than 4 trillion. Powers grow incredibly fast, so it pays to know how to work with them without calculating them. At the end of this page you'll check the Moon claim yourself.

What is a power?

A power is a repeated multiplication of the same number:

$$\underbrace{2 \cdot 2 \cdot 2 \cdot 2 \cdot 2}_{5 \text{ factors}} = 2^5 = 32$$ Diagram labeling the parts of a power: the base 7, the exponent 3, and the value of 7 cubed. 7 3 ← exponent: how many times ← base: the number that repeats 7³ = 7 · 7 · 7 = 343 (read "7 cubed")

Powers also count things in a grid or a block. A 5-by-5 grid has $5^2 = 25$ squares, and a cube built from $4 \cdot 4 \cdot 4$ blocks has $4^3 = 64$ blocks.

Move the sliders: each time the exponent goes up by 1, the result gets multiplied by the base. That's why the bars shoot up.

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Write the following repeated multiplications as a power and then calculate their numerical value. Remember that the base is the number that is repeated and the exponent…

Write the following repeated multiplications as a power and then calculate their numerical value. Remember that the base is the number that is repeated and the exponent indicates how many times it appears.

  1. a) $3 \cdot 3 \cdot 3 \cdot 3$
  2. b) $(-2) \cdot (-2) \cdot (-2)$
  3. c) $10 \cdot 10 \cdot 10 \cdot 10 \cdot 10$
  4. d) $\frac{1}{2} \cdot \frac{1}{2} \cdot \frac{1}{2}$
Solve
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We have a classic Rubik's cube. We know that on each edge (side) there are 3 small pieces. Express as a power how many small pieces make up the whole cube and calculate…

We have a classic Rubik's cube. We know that on each edge (side) there are 3 small pieces.

Express as a power how many small pieces make up the whole cube and calculate the value.

Look at the drawing to help you:

3 3 3 3³ = 27 pieces
Solve

Multiplying and dividing powers with the same base

$2^3 \cdot 2^4 = (2 \cdot 2 \cdot 2) \cdot (2 \cdot 2 \cdot 2 \cdot 2) = 2^7$. There are 3 twos, then 4 more twos: 7 twos in all. The exponents add.

$\dfrac{5^6}{5^2} = \dfrac{5 \cdot 5 \cdot 5 \cdot 5 \cdot \cancel{5} \cdot \cancel{5}}{\cancel{5} \cdot \cancel{5}} = 5^4$. You cancel as many fives as there are on the bottom. The exponents subtract.

Diagram showing that multiplying 2 cubed by 2 to the fourth gives seven factors of 2, so the exponents add. · 222 2222 2³ 2⁴ 2³ · 2⁴ = 2³⁺⁴ = 2⁷ Count the factors: 3 + 4 = 7 twos.

A number with no visible exponent has exponent 1: $x = x^1$. So $x^2 \cdot x^6 \cdot x = x^{2+6+1} = x^9$.

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Use the properties of the product of powers with the same base to simplify these expressions and leave them as a single power. You do not need to calculate the final…

Use the properties of the product of powers with the same base to simplify these expressions and leave them as a single power. You do not need to calculate the final result, just express the resulting power.

  1. a) $5^3 \cdot 5^4$
  2. b) $(-3)^2 \cdot (-3)^5$
  3. c) $x^2 \cdot x^6 \cdot x$
  4. d) $10^3 \cdot 10^2 \cdot 10^4$
Solve
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Apply the property of the quotient (division) of powers with the same base to reduce the following expressions to a single power. Remember that you must subtract the…

Apply the property of the quotient (division) of powers with the same base to reduce the following expressions to a single power. Remember that you must subtract the exponents.

  1. a) $\frac{7^8}{7^3}$
  2. b) $2^{12} : 2^{10}$
  3. c) $\frac{(-4)^5}{(-4)^2}$
  4. d) $\frac{a^6}{a}$
Solve
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Calculate the result of the following expression, applying the properties of powers before calculating the final value. Note carefully that all the bases are the same…

Calculate the result of the following expression, applying the properties of powers before calculating the final value. Note carefully that all the bases are the same negative number:

$$ \frac{(-3)^5 \cdot (-3)^2 \cdot (-3)}{(-3)^4} $$

Remember that when a number does not have a visible exponent, it is 1.

Solve

Zero, one, and negative exponents

What does $5^0$ mean? Zero fives multiplied? Look for a pattern. Start at $2^3$ and move one step at a time. Each step to the right divides by 2:

A row of powers of 2 from 2 cubed down to 2 to the negative third, with values 8, 4, 2, 1, 1/2, 1/4, 1/8, each step dividing by 2. 2³8 2²4 2¹2 2⁰1 2⁻¹1/2 2⁻²1/4 2⁻³1/8 Each step to the right: divide by 2

The pattern forces $2^0 = 1$, and then $2^{-1} = \tfrac{1}{2}$, $2^{-2} = \tfrac{1}{4}$, and so on. The quotient rule says the same thing: $\dfrac{5^3}{5^3} = 1$, and also $5^{3-3} = 5^0$.

Inside a fraction, a factor with a negative exponent moves across the bar and its exponent becomes positive: $\dfrac{a^{-2}}{b^{-3}} = \dfrac{b^3}{a^2}$. In this course, a final answer should have only positive exponents.

Some problems ask for an "irreducible fraction": that just means a fraction in simplest form.

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Calculate the value of the following powers taking into account the properties of the power with exponent 0 and the power with base 1. Be careful with the signs. a)…

Calculate the value of the following powers taking into account the properties of the power with exponent 0 and the power with base 1. Be careful with the signs.

  1. a) $5^0$
  2. b) $23^1$
  3. c) $1^{15}$
  4. d) $(-8)^0$
  5. e) $123^0 + 1^{20}$
Solve
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Work out and simplify the following expression using the properties of powers with a rational base. Express the result as an irreducible fraction with a positive…

Work out and simplify the following expression using the properties of powers with a rational base. Express the result as an irreducible fraction with a positive exponent:

$$ \left[ \left( \frac{2}{5} \right)^{-2} \cdot \left( \frac{2}{5} \right)^5 \right] : \left( \frac{5}{2} \right)^2 $$

Hint: Notice that the last fraction has its base inverted with respect to the first two.

Solve
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Simplify the following algebraic expression using the properties of powers. The final result must not have negative exponents: $$ \frac{a^3 \cdot b^{-4} \cdot…

Simplify the following algebraic expression using the properties of powers. The final result must not have negative exponents:

$$ \frac{a^3 \cdot b^{-4} \cdot a^{-2}}{a^5 \cdot b^{-6}} $$
Solve

Power of a power and the same exponent

$(3^2)^4 = 3^2 \cdot 3^2 \cdot 3^2 \cdot 3^2 = 3^{2+2+2+2} = 3^8$. Four groups of two threes: the exponents multiply.

$2^3 \cdot 5^3 = (2 \cdot 2 \cdot 2)(5 \cdot 5 \cdot 5) = (2 \cdot 5)(2 \cdot 5)(2 \cdot 5) = 10^3$. With the same exponent, you multiply the bases.

Grouping diagram: four groups of 3 times 3 show a power of a power, and three groups of 2 times 5 show a product with a common exponent. 3 · 33 · 33 · 33 · 3 (3²)⁴ = 3⁸ 2 · 52 · 52 · 5 2³ · 5³ = 10³

Perimeter and area are good places to use these. A perimeter adds the sides, so the factor 4 stays in front. An area multiplies the side by itself, so you square the power.

The perimeter merged into one power only because 4 is a power of 2. With a different base, the factor 4 can't be absorbed. Suppose a square has side $3^4$ inches. The perimeter is $4 \cdot 3^4$ in., which equals $324$ in. The powers of 3 stay together as $3^4$, and the 4 is not a power of 3, so it sits in front as a factor. The area, on the other hand, is a single power of 3: $(3^4)^2 = 3^8$ in.² (which is $6{,}561$ in.²).

So when a leftover factor (like 4 or 6) is not a power of your base, keep it as a factor in front of the power instead of forcing it inside.

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Simplify the following expressions using the property of the power of a power. You must leave the result expressed as a single power. a) $(3^2)^4$ b) $(x^3)^5$ c)…

Simplify the following expressions using the property of the power of a power. You must leave the result expressed as a single power.

  1. a) $(3^2)^4$
  2. b) $(x^3)^5$
  3. c) $((-2)^2)^3$
  4. d) $((a^2)^3)^4$
Solve
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In these cases, the bases are different but the exponents are the same. Apply the corresponding properties to group the bases and express the result as a single power.…

In these cases, the bases are different but the exponents are the same. Apply the corresponding properties to group the bases and express the result as a single power.

  1. a) $2^3 \cdot 5^3$
  2. b) $12^4 : 4^4$
  3. c) $(-2)^5 \cdot 3^5$
  4. d) $\frac{20^2}{5^2}$
Solve
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We have a square whose side measures $3^4$ inches. 1. Express the perimeter of the square as a single power of base 3 (you do not need to calculate the final number,…

We have a square whose side measures $3^4$ inches.

  1. Express the perimeter of the square as a single power of base 3 (you do not need to calculate the final number, just the power).

  2. Express the area of the square as a single power of base 3.

PERIMETER P = 4 · l AREA A = l² l = 3⁴ in. l = 3⁴ in.
Solve

Simplifying with prime factors

When the bases are different, the trick is to break them into prime factors so equal bases appear.

Factor tree of 360 showing that 360 equals 2 cubed times 3 squared times 5. 360 2180 290 245 = 3² · 5 360 = 2³ · 3² · 5 factor tree: keep dividing by primes
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Simplify the following operation and express the result as a single power of base 2. To do this, you will first have to decompose the bases that are not prime numbers…

Simplify the following operation and express the result as a single power of base 2. To do this, you will first have to decompose the bases that are not prime numbers into prime factors:

$$ 16 \cdot 2^5 \cdot 4^3 $$
Solve
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Simplify the following numerical fraction by first decomposing the bases into prime factors and then applying the properties of powers: $$ \frac{15^2 \cdot 4^2}{6^3…

Simplify the following numerical fraction by first decomposing the bases into prime factors and then applying the properties of powers:

$$ \frac{15^2 \cdot 4^2}{6^3 \cdot 10^2} $$
Solve

Combining the rules

Most real problems mix several rules. A good plan keeps you from getting lost:

Decision guide: same base, add or subtract exponents; same exponent, combine the bases; nothing in common, factor into primes first. Same base →× add exponents · ÷ subtract exponents Same exponent →combine the bases, keep the exponent Nothing in common →factor into primes first

Work inside parentheses first, then apply the outside exponent, then clear negative exponents.

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Simplify the following expressions fully by combining the properties of powers you have learned (product and quotient of equal bases). Express the result as a single…

Simplify the following expressions fully by combining the properties of powers you have learned (product and quotient of equal bases). Express the result as a single power.

  1. a) $\frac{2^5 \cdot 2^3}{2^4}$
  2. b) $\frac{x^7}{x^2 \cdot x^3}$
  3. c) $(3^2 \cdot 3^4) : 3^5$
  4. d) $\frac{10^6 \cdot 10^2}{10^8}$
Solve
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Simplify the following expression until you obtain a single power with a positive prime base. To do this, you will need to apply the properties of powers, decompose the…

Simplify the following expression until you obtain a single power with a positive prime base. To do this, you will need to apply the properties of powers, decompose the bases into prime factors, and be very careful with signs and negative exponents.

$$ \frac{(-2)^4 \cdot (2^3)^{-2} \cdot 16}{\left(\frac{1}{2}\right)^3 \cdot (-8)^{-2}} $$

Remember that decomposing numbers like 16 and 8 into base 2 is the first key step.

Solve
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Simplify the following algebraic expression using the properties of powers. The final result must not have negative exponents or brackets. $$ \left( \frac{a^{-2} \cdot…

Simplify the following algebraic expression using the properties of powers. The final result must not have negative exponents or brackets.

$$ \left( \frac{a^{-2} \cdot b^3}{a \cdot b^{-1}} \right)^{-3} : \left( \frac{a^3}{b^2} \right)^2 $$
Solve

Equations with exponents and comparing powers

If two powers with the same base (a positive number other than 1) are equal, their exponents must be equal: if $3^x = 3^5$, then $x = 5$. So the plan for an equation is: get the same base on both sides, combine, then set the exponents equal.

Three-step flow for exponent equations: get the same base, equate exponents, solve for x. Same base 22x+3 = 29 → Equate exponents 2x + 3 = 9 → Solve x = 3

Comparing big powers without a calculator

To order powers, make them share something:

  • Same exponent: the bigger base wins.

  • Same base (greater than 1): the bigger exponent wins.

If neither matches, rewrite using the GCF of the exponents (some problems call this the "highest common factor"). For $2^{15}$ and $3^{10}$, the GCF of 15 and 10 is 5:

$$2^{15} = (2^3)^5 = 8^5 \qquad 3^{10} = (3^2)^5 = 9^5$$

Same exponent, so compare the bases: $8 < 9$, which means $2^{15} < 3^{10}$.

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Calculate the value of the unknown $x$ in each of the following equalities, using the properties of powers to equate the exponents: a) $5^x \cdot 5^3 = 5^9$ b)…

Calculate the value of the unknown $x$ in each of the following equalities, using the properties of powers to equate the exponents:

  1. a) $5^x \cdot 5^3 = 5^9$
  2. b) $(3^4)^x = 3^{12}$
  3. c) $\frac{7^8}{7^x} = 7^2$
Solve
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Calculate the value of the unknown $x$ in the following exponential equation, using the properties of powers to group terms. All bases can be expressed as powers of the…

Calculate the value of the unknown $x$ in the following exponential equation, using the properties of powers to group terms. All bases can be expressed as powers of the same prime number.

$$ 27^2 \cdot 9^{-x} = \frac{1}{3^x \cdot 81} $$

Hint: Transform all bases to base 3 before operating on the exponents.

Solve
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Without using a calculator to find the final value, order the following numbers from smallest to largest. To do this, you will need to find a common exponent or a common…

Without using a calculator to find the final value, order the following numbers from smallest to largest. To do this, you will need to find a common exponent or a common base that allows you to compare them mentally.

$$ A = 2^{45} \quad ; \quad B = 3^{36} \quad ; \quad C = 5^{18} $$

Help: Try to express all the exponents as multiples of the same number (find the highest common factor of the exponents).

Solve

Powers in geometry and repeated change

Powers describe area and volume. If a square has side $s$, its area is $s \cdot s = s^2$. If a cube has edge $e$, its volume is $e^3$ and its surface area is $6e^2$.

A square with side s and area s squared, next to a cube with edge e, volume e cubed and surface area 6 times e squared. s Area = s · s = s² e Volume = e · e · e = e³ Surface area = 6 · e²

To go backwards from a volume to an edge, ask: "what number, cubed, gives this?" If $e^3 = 3^{12}$, then $e = 3^4$, because $(3^4)^3 = 3^{12}$. Notice that $27 = 3^3$, so $27^4 = (3^3)^4 = 3^{12}$.

This idea is behind fractals too. If every step multiplies a quantity by the same fraction, after $n$ steps the quantity has been multiplied by that fraction raised to the power $n$.

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Observe the following sequence of figures generated by a fractal process. 1. We start with a solid square of side 1 foot (Iteration 0). 2. We divide the square into 4…

Observe the following sequence of figures generated by a fractal process.

  1. We start with a solid square of side 1 foot (Iteration 0).

  2. We divide the square into 4 equal squares and remove the top right one (Iteration 1).

  3. We repeat the process with each of the 3 remaining squares (Iteration 2).

Calculate the total area (the sum of the areas of the black squares) in Iteration 5. Express the result as a single power.

1 ft Iteration 0 A₀ = 1 × 3/4 Iteration 1 A₁ = 3/4 × 3/4 Iteration 2 A₂ = (3/4)² ? Iteration 5 A₅ = ?
Solve
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A giant Rubik's cube is made up of small unit cubes. We know that the total volume of the large cube is $27^4$ cubic units. 1. Express the length of the edge of the…

A giant Rubik's cube is made up of small unit cubes. We know that the total volume of the large cube is $27^4$ cubic units.

  1. Express the length of the edge of the large cube as a power of base 3.

  2. If we paint the outer face of each unit cube red, what is the total area painted red on the entire giant cube? Express the result as a power of base 3.

(Remember that the large cube has 6 faces and the area of a face is side $\cdot$ side).

Solve

Powers of 2 and powers of 10

Computer storage

A bit is 0 or 1, so storage units go up by powers of 2:

Unit In bytes
1 KB $2^{10}$
1 MB $2^{10} \cdot 2^{10} = 2^{20}$
1 GB $2^{30}$
1 TB $2^{40}$
1 PB $2^{50}$

To find how many files fit, divide the total capacity by the file size, and subtract exponents.

Powers of 10 and scientific notation

A number in scientific notation looks like $a \times 10^n$ with $1 \le a < 10$. (Some problems call this standard form.) Powers of 10 follow the same exponent rules, so you can multiply, divide, and simplify them quickly.

To add or subtract, first rewrite the terms with the same power of 10, then add the front numbers. The power of 10 stays the same.

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An external hard drive has a storage capacity of 1 TB (Terabyte). Knowing that the approximate equivalents in the binary system are: $1 \text{ TB} = 2^{10} \text{ GB}$…

An external hard drive has a storage capacity of 1 TB (Terabyte). Knowing that the approximate equivalents in the binary system are:

  • $1 \text{ TB} = 2^{10} \text{ GB}$

  • $1 \text{ GB} = 2^{10} \text{ MB}$

If a high-quality photograph takes up $2^4$ MB, how many photographs fit on the hard drive in total? Express the result as a power of base 2.

1 TB × 2¹⁰ 2¹⁰ GB × 2¹⁰ 2²⁰ MB 2⁴ MB Capacidad Total: 2²⁰ MB 2⁴ 2⁴ 2⁴ ... 2⁴ ¿Número de fotos? = 2²⁰ ÷ 2⁴
Solve
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A cloud data storage server has a total capacity of 16 Petabytes (PB). Knowing that computing equivalents are powers of 2 (not 10) according to the following table:…

A cloud data storage server has a total capacity of 16 Petabytes (PB). Knowing that computing equivalents are powers of 2 (not 10) according to the following table:

  • $1 \text{ KB} = 2^{10} \text{ bytes}$

  • $1 \text{ MB} = 2^{10} \text{ KB}$

  • $1 \text{ GB} = 2^{10} \text{ MB}$

  • $1 \text{ TB} = 2^{10} \text{ GB}$

  • $1 \text{ PB} = 2^{10} \text{ TB}$

If a high-resolution photograph file takes up $2^{24}$ bytes, how many photographs fit on the server in total? Express the result as a power of base 2.

PB TB GB MB KB B ×2¹⁰ ×2¹⁰ ×2¹⁰ ×2¹⁰ ×2¹⁰ Server 16 PB Photograph 2²⁴ B ? How many?
Solve
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Calculate the exact value of the following combined operation, first applying the properties of powers and transforming to standard form before operating. $$ \frac{ 3,5…

Calculate the exact value of the following combined operation, first applying the properties of powers and transforming to standard form before operating.

$$ \frac{ 3,5 \cdot 10^{-5} + 150 \cdot 10^{-7} }{ 0,02 \cdot 10^4 \cdot (10^{-2})^3 } $$

Express the final result in standard form.

Solve

Back to the paper: a sheet of paper is about $0.004$ in. thick. After 42 folds the stack is $0.004 \cdot 2^{42} \approx 0.004 \cdot (4.4 \times 10^{12}) \approx 1.76 \times 10^{10}$ inches, which is about 278,000 miles. The Moon is only about 239,000 miles away, so the stack passes it.

Summary

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