A Level Mathematics AQA

Proof

Introduction to Proof

• Proof is a logical argument that conclusively demonstrates the truth of a statement.
• In mathematics, it's used to unequivocally confirm that a statement is true for all cases, not just some examples.

Direct Proof

• A direct proof is a type of proof where the conclusion is stated directly.
• In a direct proof, the argument moves forward in a clear, straightforward line.
• Direct proofs often take the form "If A, then B" or "B because A".

Proof by Contradiction

• Proof by contradiction, also known as reductio ad absurdum, is where you assume the opposite of what you're trying to prove, then show that this leads to an absurd situation.
• This type of proof can be very powerful because it contradicts the initial false assumption.
• Often used when the direct proof seems too complex or isn't feasible.

Mathematical Induction

• Mathematical induction is a method of proof used to establish a claim about all natural numbers.
• Contains two parts: base case and induction step. The base case shows the statement holds for a particular number, often 1. The induction step shows that if the statement holds for some number 'n', then it holds for 'n+1'.
• This can also be used to prove claims about objects other than natural numbers, like geometric figures or sentences in formal languages.

Set Theory and Proof

• Set theory is often used in proofs, particularly proofs about numbers.
• Sets can prove mathematical propositions that are true for a range of numbers.
• Venn diagrams and Euler diagrams are visual tools that can be used in set theory proofs.

Spotting Errors in Proof

• As well as constructing proofs, you need to be able to critically examine proofs for errors, either in structure or logical reasoning.
• Common errors include incorrect assumptions, misapplication of a mathematical theorem or law, and false inferences.
• Being able to spot these errors is an important skill in mathematical proof.

Using Proof in Real World Applications

• Mathematical proof isn't just about abstract concepts – it can also relate to real world applications.
• For instance, it can be used to prove the validity of algorithm, or that certain variables in physics or engineering formulas are indeed true.
• Being able to apply proof to real world problems is an important skill for future mathematicians and engineers.