CS285 · Annotated SlidesChapter 5 — Mathematical Induction and Recursion
Chapter 5 · Annotated slides

Mathematical Induction and Recursion

The principle of mathematical induction, its template, proofs of summation formulas, inequalities and divisibility, conjecturing a formula, and recursively defined functions.

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Slide 1: Slide 1
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    Chapter Summary

    Mathematical Induction

    1.

    Examples of Proof by Mathematical Induction

    2.

    Recursive Definitions

    3.

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      Slide 3: Climbing an Infinite Ladder
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        Slide 4: Principle of Mathematical Induction (MI)
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        1. To prove ∀n P(n): basis P(1); inductive step ∀k (P(k) → P(k + 1)).
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        MCQ

        In an induction proof, the assumption that P(k) is true is called the:

        Slide 5: Remembering How Mathematical Domino Effect Induction Works -
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          Slide 6: Mathematical Induction
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          1. Template: state P(n) → basis → assume P(k) → show P(k + 1) → conclude.
          Slide 7: Mathematical Induction
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            Slide 8: Mathematical Induction
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            1. Sum example: 1 + 2 + … + n = n(n + 1)/2. Add (k + 1) to both sides of P(k).
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            Written

            Prove 1 + 2 + … + n = n(n + 1)/2 for n ≥ 1.

            Slide 9: Mathematical Induction
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              Slide 10: Mathematical Induction
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                Slide 11: Mathematical Induction
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                  Slide 12: Mathematical Induction
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                  1. Divisibility example: n³ − n divisible by 3. Expand (k + 1)³ − (k + 1) = (k³ − k) + 3(k² + k).
                  Slide 13: Mathematical Induction
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                    Slide 14: Mathematical Induction
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                    1. Inequality example: 2ⁿ < n!. The basis may start later than 1 (here n ≥ 4).
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                    MCQ

                    The basis step for "2ⁿ < n! for n ≥ 4" checks:

                    Slide 15: Mathematical Induction
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                      Slide 16: Mathematical Induction
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                        Slide 17: Mathematical Induction
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                          Slide 18: Conjecturing and Proving Correct a Summation Formula
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                          1. Conjecture a formula by computing the first few values, then prove it by induction.
                          Slide 19: Mathematical Induction Example-p.316
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                            Slide 20: Proof:
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                              Slide 21: Mathematical Induction Example-p.318
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                                Slide 22: Mathematical Induction Example-p.318
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                                  5.3. Recursive Definitions

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                                    Slide 24: Recursive Definitions & Induction
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                                      Recursively Defined Functions

                                      Definition: A recursive or inductive definition of a function consists of two steps.

                                      BASIS STEP

                                      1.

                                      : Specify the value of the function at

                                      zero.

                                      RECURSIVE STEP

                                      : Give a rule for finding its value at

                                      2.

                                      an integer from its values at smaller integers.

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                                      1. Recursively defined function: basis f(0); recursive step f(n + 1) from f(n).
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                                      MCQ

                                      f(0) = 3, f(n + 1) = 2f(n) + 3. f(2) =

                                      Slide 26: Recursively Defined Functions
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                                        Slide 27: Example 2
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                                          Slide 28: Example 3
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                                            Slide 29: Example 3
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                                              Slide 30: Example 4
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                                                Slide 31: Example 4
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                                                  Slide 32: Example 5
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                                                    Slide 33: Example 5
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