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📐 Mathematics  ·  Principle of Mathematical Induction  ·  JEE

To prove n3 - n is divisible by 6 for all natural numbers n by induction, what is checked first?

Answer: That 13 - 1 = 0 is divisible by 6.

  • A That (k+1)3 - (k+1) is divisible by 6
  • B That 13 - 1 = 0 is divisible by 6
  • C That n is even
  • D That n3 is divisible by 6

Correct answer: B. That 13 - 1 = 0 is divisible by 6

Explanation: The base case checks n=1: 13 - 1 = 0, and 0 is divisible by 6 (0 = 6 x 0), so the base case holds.

Induction as a Domino ChainP(1): base case fallsP(k) knocks down P(k+1)...and so on, foreverBase case = first domino tipped; inductive step = each domino guaranteed to tip the next one

Mathematical induction works like a row of dominoes: proving the base case P(1) tips the first domino, and proving the inductive step (P(k) ⟹ P(k+1)) guarantees each domino knocks over the next - together these two facts guarantee ALL dominoes fall, without checking each one individually.

Concept context

A proof technique used to establish that a statement is true for every natural number, using a base case and an inductive step.

Read the full Principle of Mathematical Induction notes →