Limiting Cases Math Example 2

Follow the full solution, then compare it with the other examples linked below.

Example 2

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The compound interest formula is A=P(1+r/n)ntA = P(1+r/n)^{nt}. Analyse the limiting cases n=1n=1 (annual), n=12n=12 (monthly), and nโ†’โˆžn \to \infty (continuous).

Solution

  1. 1
    Annual (n=1n=1): A=P(1+r)tA = P(1+r)^t. Simple compounding once a year.
  2. 2
    Monthly (n=12n=12): A=P(1+r/12)12tA = P(1+r/12)^{12t}. More compounding events per year.
  3. 3
    Continuous (nโ†’โˆžn\to\infty): A=PertA = Pe^{rt} (derived from limโกnโ†’โˆž(1+r/n)n=er\lim_{n\to\infty}(1+r/n)^n = e^r). Maximum possible growth for rate rr.
  4. 4
    Each case is a limit: moving to more frequent compounding approaches but never exceeds PertPe^{rt}.

Answer

n=1:โ€…โ€ŠP(1+r)t;n=12:โ€…โ€ŠP(1+r/12)12t;nโ†’โˆž:โ€…โ€ŠPertn=1:\;P(1+r)^t;\quad n=12:\;P(1+r/12)^{12t};\quad n\to\infty:\;Pe^{rt}
Analysing limiting cases reveals the range of a formula's behaviour: from minimal (annual) to maximal (continuous) compounding. The continuous case is both the mathematical ideal and the simplest to work with analytically.

About Limiting Cases

Extreme values of a parameter (approaching zero, infinity, or a critical threshold) used to check formulas and reveal simplified behavior.

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