Analogical Reasoning Math Example 3

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

Example 3

easy
Exponents satisfy amโ‹…an=am+na^m \cdot a^n = a^{m+n}. By analogy with functions, what does fโˆ˜ff \circ f suggest, and how does the notation f2f^2 fit?

Solution

  1. 1
    Analogy: repeated multiplication of aa by itself nn times gives ana^n. Repeated application of ff to itself nn times gives fn=fโˆ˜fโˆ˜โ‹ฏโˆ˜ff^n = f \circ f \circ \cdots \circ f (nn times).
  2. 2
    So f2=fโˆ˜ff^2 = f \circ f (apply ff twice) and fmโˆ˜fn=fm+nf^m \circ f^n = f^{m+n} (apply ff a total of m+nm+n times).
  3. 3
    Caution: f2(x)โ‰ [f(x)]2f^2(x) \ne [f(x)]^2 in general โ€” the analogy is with composition, not multiplication.

Answer

fn=fโˆ˜fโˆ˜โ‹ฏโˆ˜fโŸn,fmโˆ˜fn=fm+nf^n = \underbrace{f \circ f \circ \cdots \circ f}_{n},\quad f^m \circ f^n = f^{m+n}
Analogical reasoning suggests that 'iteration of functions' behaves like exponentiation. The analogy holds for composition but breaks for pointwise multiplication โ€” knowing where analogies fail is as important as where they succeed.

About Analogical Reasoning

Drawing conclusions about a new situation by recognizing its structural similarity to a better-understood situation.

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