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Mathematics · unit version 1

Precalculus: local rates and polynomial evidence

Compare nearby secants without calculus, derive quadratic rate patterns, and distinguish a polynomial model from what finitely many observations establish. This focused sequence extends existing average-rate lessons; it is not a complete AP course or exam-readiness certification.

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Readiness and preparation

Check your starting point

Try these short questions on paper, then compare your reasoning. They are optional self-checks, not a placement score or a navigation requirement. Use a targeted review when useful and return with your browser’s Back control.

What does an average rate measure?

Comparing changes requires both the output change and the input interval.

Compare reasoning and find a refresher

Divide output change by input change: [f(b)−f(a)]/(b−a), for distinct inputs a and b. Its units are output units per input unit; it is not automatically the rate at either endpoint.

Review average rates and interval widths

Can a finite table determine everything between its entries?

A difference pattern supports a candidate model but does not prove a unique underlying function.

Compare reasoning and find a refresher

No. Different functions can agree at every listed input while differing between them or outside the sampled interval. State the model assumptions and check new observations.

Review tables, rules and graph evidence

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Rate and polynomial evidence: mixed practice

The mixed assessment has separate response history and review criteria; it does not change lesson participation records.

Lesson sequence

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  1. Compare local change at two inputs

    Lesson details and objectives

    Use nearby interval slopes to compare change while keeping output sign, rate sign and rate trend distinct.

    • Calculate and compare nearby secants at two specified inputs using several positive interval widths.
    • Distinguish a function’s level, its direction of change and the trend in its average rates.
    • Explain what finite secants and uncertain graph readings can and cannot establish about local behavior.

    7 practice tasks.

  2. Derive and use quadratic rate patterns

    Lesson details and objectives

    Explain constant changes in secant rates algebraically, then keep restricted-domain extrema distinct from whole-polynomial end behavior.

    • Derive a(2x+h)+b for the interval rate of ax²+bx+c when h is nonzero.
    • Connect equal-step first and second differences with quadratic coefficients and changing average rates.
    • Use completed-square form for extrema on a stated interval and distinguish them from end-limit statements.

    8 practice tasks.

  3. Read finite differences without overclaiming a model

    Lesson details and objectives

    Test equally spaced patterns, repair unequal-spacing comparisons and construct distinct functions that fit the same finite observations.

    • Compute equal-step finite-difference tables and connect their patterns to candidate polynomial degrees.
    • Explain why unequal input spacing breaks raw-difference degree rules.
    • Construct polynomial alternatives through all sampled points and distinguish fitted evidence from global shape or end behavior.

    6 practice tasks.