Vol. 5 · One step at a time

Sequences and Mathematical Induction

A companion to 《数列与数学归纳法》 by Shan Zun · 15 stops ·

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  1. Ch. 1The First Principle of InductionKnock over the first domino and make each one topple the next. All of them fall.MethodM3
  2. Ch. 2The Second Principle of InductionTo prove P(k+1), use all earlier cases, not just P(k). You may need more bases.MethodM3
  3. Ch. 3Well-Ordering and Infinite DescentPositive integers cannot shrink forever, so no solution can make a smaller one.MethodM2M6M19
  4. Ch. 4General Terms and SumsSplit each term as “this minus next”; the middle cancels, only the ends survive.SkillM9M12M16
  5. Ch. 5Arithmetic and Geometric SequencesArithmetic: add it in reverse. Geometric: multiply by q, shift and subtract.Concept
  6. Ch. 6Higher-Order Arithmetic Sequences and DifferencesSubtract neighbors until a row is constant, then add back up to extend the list.SkillM10
  7. Ch. 7Recursive SequencesLinear recurrences: solve the characteristic equation, fit the initial values.SkillM1M13
  8. Ch. 8Periodic SequencesWhen finitely many states decide the next term, a state repeats and it cycles.ConceptM4M7M19
  9. Ch. 9The Fibonacci SequenceDomino tilings count Fibonacci numbers; one cut gives its addition formula.ConceptM7M13
  10. Ch. 10Several Proofs of the AM–GM InequalityStuck at n ⇒ n+1? Double 2, 4, 8, …, then fill back down: backward induction.MethodM3
  11. Ch. 11Choosing the Right Step SizeEach domino knocks over the k-th next: a big step, but k base cases to check.MethodM3
  12. Ch. 12Choosing What to Induct OnSeveral variables? See which smaller cases the step needs, then choose.MethodM3
  13. Ch. 13Changing the StatementStuck? Prove more: a stronger claim gives a stronger hypothesis for n → n+1.MethodM3M15
  14. Ch. 14Guess, Then ProveWork out small cases, guess a formula, then nail it down by induction.MethodM3M13
  15. Ch. 15Existence Problems for SequencesShow existence by building it term by term, or show that “none” is absurd.MethodM4M14M18