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Math · Grade 8 Math

Chapter 7: Exponents and Scientific Notation

Laws of Exponents

Count the factors and the rules explain themselves.

Lesson
1
Time
About 19 minutes
0 of 8 done

Step 1: Let's Learn

Read it, or press Listen and follow the words.

2³ × 2⁴ is three 2s times four 2s, which is seven 2s. So the exponents add.

Dividing subtracts

2⁵ ÷ 2² cancels two of the 2s, leaving three. So the exponents subtract.

Why anything to the power 0 is 1

2³ ÷ 2³ is 1, and the rule gives 2⁰. So 2⁰ must be 1.

Negative exponents

2⁻² is 1 ÷ 2², which is 1/4. Carrying the pattern below zero forces it.

The laws are just counting factors

x³ × x² is (x·x·x) × (x·x), five factors in all, so x⁵. The rule "add the exponents" is a shortcut for counting. Writing the factors out once makes every exponent law obvious rather than arbitrary.

Dividing subtracts

x⁵ ÷ x² has five factors on top and two below; two cancel, leaving three. So x⁵ ÷ x² = x³. Subtracting exponents is cancellation, which is why the rule only works when the bases are the same.

A power of a power multiplies

(x²)³ means x² × x² × x², which is six factors: x⁶. The exponents multiply because you have three groups of two. Again, expanding once shows why, and the shortcut follows.

The laws need the same base

x³ × y² cannot be simplified — the factors are different things. All the exponent laws require a common base, and applying them across different bases is the most common error in the topic.

Step 2: Try It Yourself

Tap and try it out.

A square number really is a square. Set both sides equal.

4 × 4 = 16

4 rows of 4 makes 16.

Step 3: Watch an Example

One step at a time.

Watch Ana Simplify 3² × 3⁴

Ana multiplies two powers of the same base.

  1. Step 1

    She counts the factors: two 3s times four 3s.

Step 4: Your Turn

Practice makes it stick.

The Product

Problem 1 of 2

2³ × 2² = 2 to what power?

The Quotient

Problem 2 of 2

5⁷ ÷ 5⁴ = 5 to what power?

Count the Factors

1 of 4

4² × 4³ = 4 to what power?

2 of 4

6⁸ ÷ 6³ = 6 to what power?

3 of 4

What is 7⁰?

4 of 4

What is 2⁻² as a fraction with top 1? Give the bottom number.

Step 5: Quick Check

Show what you know.

Question 1 of 2

3⁵ × 3² = 3 to what power?

Question 2 of 2

Why does multiplying powers add the exponents?

What You Learned

  • Multiplying powers of the same base adds the exponents.
  • Dividing subtracts them.
  • Anything to the power 0 is 1, and a negative exponent is a reciprocal.