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AP® Calculus AB · Unit 7 · Topic 7.2

Verifying Solutions for Differential Equations: Topic Checklist (Calculus AB 7.2)

Specific “I can…” statements for verifying solutions of differential equations, each linked to the guide section and practice question that tests it.

Work through the list without notes or a calculator. If you cannot do a statement, follow its link, then come back. Guide = study guide; Practice = practice questions. This topic is shared by Calculus AB and Calculus BC.

Understanding

  • I can explain what it means for a function to be a solution of a differential equation on an interval. (Guide: “What ‘solution’ means here”)
  • I can explain why agreement at one input value does not prove a solution, but disagreement at one value disproves it. (Guide: “Why one point is not enough”; Practice Q7(c))
  • I can explain why a differential equation can have infinitely many solutions, using a family with a constant C. (Guide: “Infinitely many solutions” and Figure 1; Practice Q4, Q5(d))
  • I can explain why a formula is a solution only on intervals where it is defined and differentiable. (Guide: Worked example 3; Practice Q6(c))

Skills

  • I can verify a first-order solution by setting out the left side and right side separately. (Guide: Worked example 1; Practice Q1, Q3)
  • I can verify a second-order solution, finding y″ with the chain rule. (Guide: “Second-order equations”; Practice Q5)
  • I can find the values of r that make y = e^(rx) a solution. (Guide: Worked example 2; Practice Q2)
  • I can find unknown constants in a given form by matching coefficients. (Practice Q7(a))
  • I can show a family with an arbitrary constant solves an equation for every value of the constant. (Guide: Worked examples 1 and 3; Practice Q6(b), Q7(b))

Reasoning

  • I can spot a constant solution and say whether the family includes it. (Guide: Worked example 3; Practice Q6(d))
  • I can explain why adding a constant to a solution may give a non-solution. (Guide: Worked example 2; Practice Q5(c))
  • I can check that a solution’s shape matches what the equation says about the rate. (Guide: Worked example 1 and Figure 1)

All ticked? Move on to Topic 7.3, Sketching Slope Fields, or return to the Calculus AB roadmap or the Calculus BC roadmap.

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