Unit 6 · 9th Grade Mathematics

Exponents &
Exponential Functions.

Laws of exponents, exponential growth and decay, and geometric sequences.

Start studyingTopic B: Exponential Functions

Unit 6 — Lesson Video

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Topic A: Laws of Exponents

Lessons 1–4 · Product, quotient, power, and negative exponent rules.

01–02 — Lessons 1–2

Exponent Rules

  • Product rule: aᵐ · aⁿ = aᵐ⁺ⁿ
  • Quotient rule: aᵐ / aⁿ = aᵐ⁻ⁿ
  • Power rule: (aᵐ)ⁿ = aᵐⁿ
  • Zero exponent: a⁰ = 1 (a ≠ 0)
  • Negative exponent: a⁻ⁿ = 1/aⁿ
  • Fraction base: (a/b)ⁿ = aⁿ/bⁿ
x³ · x⁵ = x⁸  ·  (2x²)³ = 8x⁶  ·  x⁻² = 1/x²
Practice — Lessons 1–2
Q1 · Short Answer

Simplify: x⁴ · x⁷. Write as xⁿ.

Q2 · Multiple Choice

What is 5⁰?

03–04 — Lessons 3–4

Scientific Notation

  • Scientific notation: a × 10ⁿ, where 1 ≤ a < 10.
  • Large numbers: move decimal left → positive exponent.
  • Small numbers: move decimal right → negative exponent.
  • Multiply: multiply the a-values, add the exponents.
  • Divide: divide the a-values, subtract the exponents.
0.000045 = 4.5 × 10⁻⁵  ·  (3×10⁴)(2×10³) = 6×10⁷
Practice — Lessons 3–4
Q3 · Multiple Choice

Write 67,000 in scientific notation.

Q4 · Short Answer

(4 × 10³) × (2 × 10⁵) = ? Write in scientific notation.

Topic B: Exponential Functions

Lessons 5–9 · Graphing, growth, decay, and applications.

05–07 — Lessons 5–7

Exponential Growth & Decay

  • General form: f(x) = a · bˣ
  • a: initial value (y-intercept). b: base (growth/decay factor).
  • b > 1: exponential growth. 0 < b < 1: exponential decay.
  • Percent change: growth rate r means b = 1 + r. Decay: b = 1 − r.
  • No x-intercept (for a > 0). Asymptote at y = 0 (for standard exponential).
Population decreases 15%/yr from 1000: f(t) = 1000·(0.85)ᵗ. After 4 yr: f(4) ≈ 522.
Practice — Lessons 5–7
Q5 · Multiple Choice

A quantity grows by 20% each year starting at 500. What is the base b?

Q6 · Short Answer

Using f(t) = 400·(0.5)ᵗ, what is f(2)?

08–09 — Lessons 8–9

Geometric Sequences & Comparing Function Types

  • Geometric sequence: multiply by constant ratio r each term.
  • aₙ = a₁ · r^(n−1)
  • vs. arithmetic sequence: arithmetic adds a constant difference.
  • Geometric sequences are modeled by exponential functions.
  • Comparing: exponential eventually overtakes linear and quadratic.
Sequence: 3, 6, 12, 24 → r = 2 → a₅ = 3·2⁴ = 48
Practice — Lessons 8–9
Q7 · Multiple Choice

Which sequence is geometric?

Q8 · Short Answer

Find the 5th term of the sequence 2, 6, 18, 54, …