AP Precalculus · Unit 1: Polynomial and Rational Functions ·  Lesson 1.6

Polynomial Functions and End Behavior

Limits at the ends and the leading term  ·  Approx. 2–3 class days

Starringleading term decides the endslim x→∞ p(x) = ±∞

Use this as a quick reference for limit notation at both ends, the leading term dominating, the four end-behavior patterns, and reading ends from graphs.

Polynomial Functions and End Behavior infographic

🧭 Plot Summary

Lesson 1.5 found where a polynomial hits zero. Now zoom all the way out. As x increases or decreases without bound, the outputs of a nonconstant polynomial either increase or decrease without bound, and you write that with limit notation such as limx→∞ p(x) = ∞. The reason is that the leading term dominates every lower-degree term once the inputs are large. So just two facts decide both ends: whether the degree is even or odd, and whether the leading coefficient is positive or negative.

What you'll do in this lesson

  • Describe what a nonconstant polynomial does as x increases without bound.
  • Describe what it does as x decreases without bound, using limit notation.
  • Explain why the leading term dominates the lower-degree terms.
  • Use the degree and the sign of the leading term to predict both ends.
  • Find the leading term from a factored form without multiplying out.
  • Read end behavior from a graph and work backward to the degree and sign.

Why it matters

Long-run behavior is the question behind every model: where does the population, the cost, or the height go if the model keeps running? The ends tell you whether a polynomial model can be trusted far from the data. Lesson 1.7 uses the same dominance idea on a quotient of two polynomials.

✅ Self-Check Before You Move On

Check off each item as you get there. These aren't grades — they're your own signal.