1.3.6

Disproof by Counter Example

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Proofs and Counter Examples

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General numbers in proofs

  • If we are proving something involving an even number, use 2n.
  • If we are proving something involving an odd number, use 2n + 1.
  • Consecutive numbers are shown by n, n + 1, n + 2, ... etc
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Counter examples

  • A counter example is the simplest way to prove a statement is wrong.
  • You only need one counter example to show something is wrong.
  • To disprove the statement ‘The product of two primes is always odd':
    • Use the counter example of the primes 2 and 3 whose product is 6 which is even.

Jump to other topics

1Proof

2Algebra & Functions

2.1Powers & Roots

2.2Quadratic Equations

2.3Inequalities

2.4Polynomials

2.5Graphs

2.6Functions

2.7Transformation of Graphs

2.8Partial Fractions (A2 Only)

3Coordinate Geometry

4Sequences & Series

5Trigonometry

6Exponentials & Logarithms

7Differentiation

8Integration

9Numerical Methods

10Vectors

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