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Lesson 9 of 16 · about 14 min

Contrapositive and cases

When a direct proof gets stuck, two tools help. Prove the contrapositive instead (it means the same thing), or split the problem into cases and handle each one. You'll prove that if n² is even then n is even, and use remainders to learn which digits a perfect square can end in.

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In this lesson you'll learn:

  • Proof by contrapositive
  • Proof by cases

Free to try in F05 Logic & Proofs:

The first 3 lessons of every course are free, no account needed.