Mathematics (2019) Grade(s): 09-12 - Precalculus

MA19.PRE.15

Derive the formula for the sum of a finite geometric series (when the common ratio is not 1), and use the formula to solve problems, extending to infinite geometric series.

COS Examples

Examples: calculate mortgage payments; determine the long-term level of medication if a patient takes 50 mg of a medication every 4 hours, while 70% of the medication is filtered out of the patient’s blood.

Unpacked Content

Knowledge

Students know:
  • Characteristics of a geometric series.
  • Techniques for performing algebraic manipulations and justifications for the equivalence of the resulting expressions.

Skills

Students are able to:
  • Identify the regularity that exists in a series as being that which defines it as a geometric series.
  • Accurately perform the procedures involved in using geometric series to solve contextual problems,
  • Explain with mathematical reasoning why each step in the derivation of the formula for the sum of a finite geometric series is legitimate, including explaining why the formula does not hold for a common ratio of 1.

Understanding

Students understand that:
  • When each term of a geometric series is multiplied by a value, the result is a new geometric series.
  • When many problems exist with the same mathematical structure, formulas are useful generalizations for efficient solution of problems, (e.g., mortgage payment calculation with geometric series).

Vocabulary

  • Geometric series (finite and infinite)
  • Common ratio
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