Learn on PengiIllustrative Mathematics, Grade 8Chapter 7: Exponents and Scientific Notation

Lesson 2: Exponent Rules

In this Grade 8 Illustrative Mathematics lesson from Chapter 7: Exponents and Scientific Notation, students discover and apply the product of powers rule, learning that multiplying powers of 10 is equivalent to adding their exponents (for example, 10⁵ · 10² = 10⁷). Students build this understanding by expanding expressions in a table, then generalize the rule as 10ⁿ · 10ᵐ = 10⁽ⁿ⁺ᵐ⁾. The lesson also uses the product rule to explore the meaning of the zero exponent, establishing why 10⁰ equals 1.

Section 1

The Power of a Power Rule for Exponents

Property

To raise a power to another power, you multiply the exponents. The general form is (am)n=amn(a^m)^n = a^{m \cdot n}.

Examples

  • (23)4=234=212(2^3)^4 = 2^{3 \cdot 4} = 2^{12}
  • (105)2=1052=1010(10^5)^2 = 10^{5 \cdot 2} = 10^{10}
  • (x6)3=x63=x18(x^6)^3 = x^{6 \cdot 3} = x^{18}

Explanation

The power of a power rule simplifies expressions where an exponential term is raised to another exponent. For example, (23)4(2^3)^4 means you are multiplying 232^3 by itself four times: 232323232^3 \cdot 2^3 \cdot 2^3 \cdot 2^3. Using the product rule, you would add the exponents: 23+3+3+3=2122^{3+3+3+3} = 2^{12}. This rule provides a shortcut by simply multiplying the two exponents, 343 \cdot 4, to get the same result.

Section 2

The Product Rule of Exponents

Property

For any real number aa and natural numbers mm and nn, the product rule of exponents states that

aman=am+na^m \cdot a^n = a^{m+n}

Examples

  • To simplify g4g2g^4 \cdot g^2, we add the exponents: g4+2=g6g^{4+2} = g^6.
  • To simplify (5)4(5)(-5)^4 \cdot (-5), we recognize that (5)(-5) is (5)1(-5)^1. So, we have (5)4+1=(5)5(-5)^{4+1} = (-5)^5.
  • We can combine multiple terms: y3y6y2=y3+6+2=y11y^3 \cdot y^6 \cdot y^2 = y^{3+6+2} = y^{11}.

Explanation

When multiplying terms with the same base, keep the base and add the exponents. This is a shortcut for counting all the individual factors. For example, x2x3x^2 \cdot x^3 means (xx)(xxx)(x \cdot x) \cdot (x \cdot x \cdot x), which is simply x5x^5.

Section 3

The Quotient Rule for Exponents

Property

To divide two powers with the same base, subtract the exponent of the denominator from the exponent of the numerator. For any non-zero number aa, and for whole numbers mm and nn where m>nm > n:

aman=amn\frac{a^m}{a^n} = a^{m-n}

Examples

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Chapter 7: Exponents and Scientific Notation

  1. Lesson 1

    Lesson 1: Exponent Review

  2. Lesson 2Current

    Lesson 2: Exponent Rules

  3. Lesson 3

    Lesson 3: Scientific Notation

Lesson overview

Expand to review the lesson summary and core properties.

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Section 1

The Power of a Power Rule for Exponents

Property

To raise a power to another power, you multiply the exponents. The general form is (am)n=amn(a^m)^n = a^{m \cdot n}.

Examples

  • (23)4=234=212(2^3)^4 = 2^{3 \cdot 4} = 2^{12}
  • (105)2=1052=1010(10^5)^2 = 10^{5 \cdot 2} = 10^{10}
  • (x6)3=x63=x18(x^6)^3 = x^{6 \cdot 3} = x^{18}

Explanation

The power of a power rule simplifies expressions where an exponential term is raised to another exponent. For example, (23)4(2^3)^4 means you are multiplying 232^3 by itself four times: 232323232^3 \cdot 2^3 \cdot 2^3 \cdot 2^3. Using the product rule, you would add the exponents: 23+3+3+3=2122^{3+3+3+3} = 2^{12}. This rule provides a shortcut by simply multiplying the two exponents, 343 \cdot 4, to get the same result.

Section 2

The Product Rule of Exponents

Property

For any real number aa and natural numbers mm and nn, the product rule of exponents states that

aman=am+na^m \cdot a^n = a^{m+n}

Examples

  • To simplify g4g2g^4 \cdot g^2, we add the exponents: g4+2=g6g^{4+2} = g^6.
  • To simplify (5)4(5)(-5)^4 \cdot (-5), we recognize that (5)(-5) is (5)1(-5)^1. So, we have (5)4+1=(5)5(-5)^{4+1} = (-5)^5.
  • We can combine multiple terms: y3y6y2=y3+6+2=y11y^3 \cdot y^6 \cdot y^2 = y^{3+6+2} = y^{11}.

Explanation

When multiplying terms with the same base, keep the base and add the exponents. This is a shortcut for counting all the individual factors. For example, x2x3x^2 \cdot x^3 means (xx)(xxx)(x \cdot x) \cdot (x \cdot x \cdot x), which is simply x5x^5.

Section 3

The Quotient Rule for Exponents

Property

To divide two powers with the same base, subtract the exponent of the denominator from the exponent of the numerator. For any non-zero number aa, and for whole numbers mm and nn where m>nm > n:

aman=amn\frac{a^m}{a^n} = a^{m-n}

Examples

Book overview

Jump across lessons in the current chapter without opening the full course modal.

Continue this chapter

Chapter 7: Exponents and Scientific Notation

  1. Lesson 1

    Lesson 1: Exponent Review

  2. Lesson 2Current

    Lesson 2: Exponent Rules

  3. Lesson 3

    Lesson 3: Scientific Notation