Raisonnement par récurrence

Mathematical induction is a proof technique that establishes the truth of a statement for all natural numbers. It works in two steps: first, verify the base case by testing the statement at an initial value, typically n = 1. Second, prove the inductive step by assuming the statement holds for an arbitrary number k and showing it also holds for k + 1. When both steps succeed, the statement is proven for all natural numbers.

The base case is the first step of mathematical induction where you verify that a formula or statement is true for the initial value, usually n = 1. You substitute this value into both sides of the equation and confirm they are equal. If the base case holds, you establish a foundation for proving the statement applies to all subsequent natural numbers.

The inductive step assumes a formula holds for an arbitrary natural number k, called the induction hypothesis. You then add the next term, k + 1, to both sides and algebraically verify the formula still holds. This demonstrates the pattern continues from k to k + 1, establishing that if the formula works for any number, it works for the next one.

Mathematical induction proves this formula by confirming both the base case and inductive step. For n = 1, the sum equals 1 and the formula yields 1(2)/2 = 1, so the base case holds. Assuming the formula works for k, adding k + 1 to both sides maintains the pattern, proving it holds for all natural numbers through the inductive step.

The induction hypothesis is the assumption made during the inductive step that a formula or statement is true for some arbitrary natural number k. This assumption is not proven initially; instead, it is used as a starting point to show the formula also holds for k + 1. By demonstrating this continuation, you validate the pattern for all natural numbers.

The domino effect illustrates mathematical induction by showing that if the first domino falls and each domino topples the next, the entire line will fall. Similarly, if a statement is true for n = 1 (first domino falls) and proving it for k implies it is true for k + 1 (each domino topples the next), then the statement holds for all natural numbers.

Yes, mathematical induction is ideal for proving formulas about sequences and series. For example, it can verify that the sum of the first n natural numbers follows a specific pattern. By confirming the base case and showing the inductive step maintains the pattern, you establish that the formula applies to all natural numbers in arithmetic sequences and other sequence-based statements.