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AP® Calculus BC · Unit 10 · Topic 10.13

Radius and Interval of Convergence of Power Series: Topic Checklist (Calculus BC 10.13)

Specific “I can…” statements for radius and interval of convergence, each linked to the guide section and practice question that shows whether you can really do it.

BC-only material. Work through the list without notes. If you cannot do a statement, follow its link, then come back. Guide = study guide; Practice = practice questions. Prerequisites (Topics 10.2, 10.5, 10.7, 10.8 and 10.9) are on the Calculus BC roadmap.

Understanding

  • I can write the general form of a power series and name its centre and coefficients. (Guide: “What a power series is”)
  • I can explain the three possible outcomes: convergence only at the centre, on an interval centred at c, or for every real x. (Guide: “Only three things can happen”; Practice Q3)
  • I can explain why the ratio test cannot decide an endpoint. (Guide: “Endpoint toolkit”)
  • I can explain why a power series with positive radius is the Taylor series of its sum. (Guide: “Power series and Taylor series”)

Skills

  • I can use the ratio test on the whole term to find a radius of convergence, including R = 0 and R = ∞. (Guide: “Finding the radius with the ratio test”; Practice Q1, Q3)
  • I can rewrite a condition such as |2x − 5| < 1 in the form |x − c| < R before reading off R. (Guide: Worked example 2)
  • I can handle series with only even powers, such as Σ x^(2n)/(4ⁿ(n + 1)). (Practice Q5)
  • I can test each endpoint with a named test (p-series, alternating series, nth term, comparison) and write the interval with correct brackets. (Guide: Worked example 1; Practice Q2, Q5, Q6(b))
  • I can find f⁽ⁿ⁾(c) from a coefficient using f⁽ⁿ⁾(c) = n! · aₙ. (Practice Q4)

Reasoning

  • I can state that term-by-term differentiation or integration keeps the radius, and retest the endpoints of the new series. (Guide: “Differentiating and integrating term by term”; Practice Q6(c)–(d))
  • I can decide where a series must converge, must diverge, or might do either, from convergence at one point and divergence at another. (Guide: “Only three things can happen”; Practice Q7)
  • I can justify each endpoint decision in a sentence that names the test and its conditions. (Practice Q6, Q7(c))

All ticked? Move on to Topic 10.14, Finding Taylor or Maclaurin series for a function, or return to the Calculus BC roadmap.

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