1.3.2

Proof by Deduction

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What is proof by deduction?

Proof by deduction is a proof that consists of using known theorems to prove a given statement is always true.

How do you prove by deduction?

How do you prove by deduction?

Proof by deduction begins with a known theorem.
We use a series of logical steps to go from the theorem to the final statement.
- You need to write out each step clearly and consider all potential cases.
This statement should either prove the conjecture is always true or that it must be false.

Example

Example

Prove that the sum of two odd numbers is even.

Assumptions

Assumptions

If $x$ and $y$ are odd, we can write them as:
- $x = 2a+1$ and $y = 2b+1$
Where $a$ and $b$ are integers.

Sum

Sum

Adding $x$ and $y$ together, we get:
- $x+y = 2a+1+2b+1 = 2a + 2b + 2$
Collecting terms in a sum like this is known to be always true, so it's a valid step in the proof.

Inspection

Inspection

In order for $x+y$ to be even, we need to be able to write it as $2c$ , where $c$ is an integer.
By inspecting the equation for $x+y$ we obtained earlier, we can rewrite it as:
- $x+y = 2a+2b+2 = 2(a+b+1)$
As $a$ and $b$ are integers, $a+b+1$ is also an integer.
This means $x+y$ is an even number, for all possible odd values of $x$ and $y$ .

Final statement

Final statement

The sum of two odd numbers is an even number.

Full proof

Full proof

1

Proof

1.1

Types of Numbers

1.1.1Whole Numbers 1.1.2The Four Rules for Positive Numbers 1.1.3Negative Numbers 1.1.4Integers 1.1.5The Four Rules for Negative Numbers 1.1.6Real Numbers 1.1.7Rational vs Irrational

1.2

Notation

1.2.1Sets 1.2.2Subsets 1.2.3Venn Diagrams 1.2.4Sets Numbers 1.2.5Notation in Mathematical Arguments

1.3

Proof

1.3.1Mathematical Proof 1.3.2Proof by Deduction 1.3.3Proving an Identity 1.3.4Polynomial Identities 1.3.5Proof by Exhaustion 1.3.6Disproof by Counter Example 1.3.7Proof by Contradiction (A2 Only)

2

Algebra & Functions

2.1

Powers & Roots

2.1.1Exponential Rules 2.1.2Rational Exponents 2.1.3Surds 2.1.4Simplify Surds 2.1.5Rationalise Denominator

2.2

Quadratic Equations

2.2.1Quadratic +/-2.2.2Factorise Quadratics 2.2.3Quadratic Formula 2.2.4Complete the Square 2.2.5Solve Quadratics Graphically 2.2.6Simultaneous Equations 2.2.7Simultaneous Quadratic Equations 2.2.8Simultaneous Equations Graphs 2.2.9Simultaneous Equations Word Problems 2.2.10Quadratic Equations of Powers

2.3

Inequalities

2.3.1Solving Inequalities 2.3.2Solving Double Inequalities 2.3.3Solving Quadratic Inequalities 2.3.4Representing Inequalities 2.3.5Graphing Inequalities 2.3.6Set Notation 2.3.7Set Notation & Inequalities

2.4

Polynomials

2.4.1Polynomials 2.4.2Adding & Subtracting Polynomials 2.4.3Remainder Theorem 2.4.4Algebraic Long Division 2.4.5Rewriting Rational Expressions

2.5

Graphs

2.5.1Graphs of Polynomials 2.5.2Simultaneous Equations Graphs 2.5.3Simultaneous Quadratic Equations 2.5.4Graphs of Proportion 2.5.5Graphs of Common Functions 1 2.5.6Graphs of Common Functions 2 2.5.7Graphs of Common Functions 3 2.5.8Proportion 2.5.9Direct Proportion 2.5.10Inverse Proportion

2.6

Functions

2.6.1Properties of Functions 2.6.2Inverse Functions 2.6.3Composite Functions

2.7

Transformation of Graphs

2.7.1Reflections 2.7.2Rotation 2.7.3Translation 2.7.4Stretches & Compressions 2.7.5Effects of Transformations 2.7.6Combinations of Transformations

2.8

Partial Fractions (A2 Only)

2.8.1Partial Fractions 2.8.2Partial Fractions with Three Linear Factors 2.8.3Partial Fractions with Three Linear Factors 2 2.8.4Partial Fractions with Repeated Factors 2.8.5Partial Fractions - Practice

3

Coordinate Geometry

3.1

Straight Lines

3.1.1y = mx +c 3.1.2Gradient & Y-intercept 3.1.3Distance-Time Graph 3.1.4Velocity-Time Graph 3.1.5Conversion Graph

3.2

Circles

3.2.1Equations of Circles centred at Origin 3.2.2Finding the Centre & Radius 3.2.3Equation of a Tangent 3.2.4Circle Theorems - Perpendicular Bisector 3.2.5Circle Theorems - Angle at the Centre 3.2.6Circle Theorems - Angle at a Semi-Circle 3.2.7Equation of a Perpendicular Bisector 3.2.8Equation of a Circumcircle 3.2.9Circumcircle of a Right-angled Triangle

3.3

Parametric Equations (A2 only)

3.3.1Parametric Equations 3.3.2Modelling with Parametric Equations

4

Sequences & Series

4.1

Binomial Expansion

4.1.1Pascal's Triangle 4.1.2Factorials 4.1.3Binomial Expansion 4.1.4Binomial Expansion & Rational Powers (A2 only)4.1.5Binomial Expansion & Rational Powers 2 (A2 only)

4.2

Sequences (A2 only)

4.2.1Nth term Rules 4.2.2Recurring Rules 4.2.3Types of Sequences 4.2.4Arithmetic Sequences 4.2.5Geometric Sequences 4.2.6Sigma Notation 4.2.7Arithmetic Series 4.2.8Geometric Series 4.2.9Sum to Infinity of a Geometric Series 4.2.10Modelling with Sequences & Series

5

Trigonometry

5.1

Using Angles

5.1.1Radians 5.1.2Arc length 5.1.3Area of Sectors 5.1.4Area of Segments

5.2

Trigonometric Functions

5.2.1Unit Circle 5.2.2Properties of Trig Functions 5.2.3Trigonometry 5.2.4Exact values 5.2.5Graphs of Trigonometric Functions 5.2.6Small Angle Approximation

5.3

Triangle Rules

5.3.1Sine Rules 5.3.2Cosine Rules 5.3.3Area of a Triangle

5.4

Trigonometric Identities

5.4.1Secant, Cosecant & Cotangent 5.4.2Pythagorean Identities 5.4.3Angle Addition Formulae 5.4.4Manipulating the Angle Addition Formulae 5.4.5Double Angle Formula

6

Exponentials & Logarithms

6.1

Exponentials & Logarithms

6.1.1Exponential Function 6.1.2Logarithms 6.1.3Properties of Logarithms 6.1.4Natural Logarithm 6.1.5Graphs of Exponents & Logarithms

6.2

Exponential Growth Decay

6.2.1Population Growth 6.2.2Depreciation 6.2.3Graphing Linear and Exponential Growth 6.2.4Interpreting Exponential Growth and Decay Graphs 6.2.5Compound Growth & Decay 6.2.6Compund Interest

7

Differentiation

7.1

Derivatives

7.1.1Gradient of a Curve 7.1.2Differentiation from First Principles 7.1.3Differentiation from First Principles - Practice 7.1.4Differentiation 7.1.5Finding derivatives 7.1.6Second Order Derivatives

7.2

Graphs & Differentiation

7.2.1Stationary Points 7.2.2Maxima & Minima 7.2.3Modelling with Differentiation 7.2.4Using Second Derivatives (A2 only)7.2.5Rate of Change (A2 only)

7.3

Differentiation With Trigonometry and Exponentials

7.3.1Differentiation with Sin & Cos 7.3.2Diff. of Exponential Functions 7.3.3Differentiation of Trig. Functions 1 (A2 only)7.3.4Differentiation of Trig. Functions 2 (A2 only)

7.4

Rules of Differetiation (A2 only)

7.4.1Chain Rule 7.4.2Product Rule 7.4.3Quotient Rule

7.5

Parametric & Implicit Differentiation

7.5.1Parametric Differentiation 7.5.2Implicit Differentiation

8

Integration

8.1

Integration

8.1.1Integration - Basics 8.1.2Integration - Definite Integrals 8.1.3Finding Functions 8.1.4Area under curves 8.1.5Area under x-axis 8.1.6Area between curves and lines

8.2

Integration (A2 Only)

8.2.1Integration - Standard Functions 8.2.2Integration - Reverse Chain Rule 8.2.3Integration by Substitution 8.2.4Integration by Parts 8.2.5Integration by Parts - Practice 8.2.6Integration by Partial Fraction 8.2.7Modelling with Differential Equations

9

Numerical Methods

9.1

Finding Solutions

9.1.1Number Iterations 9.1.2Iterations to 1 Decimal Places 9.1.3Iteration Formula 9.1.4Locating Roots 9.1.5Newton Raphson Method

9.2

Finding the Area

9.2.1Trapezium Rule

10

Vectors

10.1

2D Vectors

10.1.1Vectors - Magnitude & Direction 10.1.2Unit Vectors 10.1.3Vectors - Algebraic Operations 10.1.4Position Vectors 10.1.5Vector Proofs 10.1.6Vectors Word Questions

10.2

3D Vectors

10.2.13D Vector Magnitude 10.2.23D Vectors - Algebraic Operations 10.2.3Position Vectors 3D 10.2.43D Vectors Word Questions

10.3

Vector Proofs

10.3.1Coming Soon

Jump to other topics

1

Proof

1.1

Types of Numbers

1.1.1Whole Numbers 1.1.2The Four Rules for Positive Numbers 1.1.3Negative Numbers 1.1.4Integers 1.1.5The Four Rules for Negative Numbers 1.1.6Real Numbers 1.1.7Rational vs Irrational

1.2

Notation

1.2.1Sets 1.2.2Subsets 1.2.3Venn Diagrams 1.2.4Sets Numbers 1.2.5Notation in Mathematical Arguments

1.3

Proof

1.3.1Mathematical Proof 1.3.2Proof by Deduction 1.3.3Proving an Identity 1.3.4Polynomial Identities 1.3.5Proof by Exhaustion 1.3.6Disproof by Counter Example 1.3.7Proof by Contradiction (A2 Only)

2

Algebra & Functions

2.1

Powers & Roots

2.1.1Exponential Rules 2.1.2Rational Exponents 2.1.3Surds 2.1.4Simplify Surds 2.1.5Rationalise Denominator

2.2

Quadratic Equations

2.2.1Quadratic +/-2.2.2Factorise Quadratics 2.2.3Quadratic Formula 2.2.4Complete the Square 2.2.5Solve Quadratics Graphically 2.2.6Simultaneous Equations 2.2.7Simultaneous Quadratic Equations 2.2.8Simultaneous Equations Graphs 2.2.9Simultaneous Equations Word Problems 2.2.10Quadratic Equations of Powers

2.3

Inequalities

2.3.1Solving Inequalities 2.3.2Solving Double Inequalities 2.3.3Solving Quadratic Inequalities 2.3.4Representing Inequalities 2.3.5Graphing Inequalities 2.3.6Set Notation 2.3.7Set Notation & Inequalities

2.4

Polynomials

2.4.1Polynomials 2.4.2Adding & Subtracting Polynomials 2.4.3Remainder Theorem 2.4.4Algebraic Long Division 2.4.5Rewriting Rational Expressions

2.5

Graphs

2.5.1Graphs of Polynomials 2.5.2Simultaneous Equations Graphs 2.5.3Simultaneous Quadratic Equations 2.5.4Graphs of Proportion 2.5.5Graphs of Common Functions 1 2.5.6Graphs of Common Functions 2 2.5.7Graphs of Common Functions 3 2.5.8Proportion 2.5.9Direct Proportion 2.5.10Inverse Proportion

2.6

Functions

2.6.1Properties of Functions 2.6.2Inverse Functions 2.6.3Composite Functions

2.7

Transformation of Graphs

2.7.1Reflections 2.7.2Rotation 2.7.3Translation 2.7.4Stretches & Compressions 2.7.5Effects of Transformations 2.7.6Combinations of Transformations

2.8

Partial Fractions (A2 Only)

2.8.1Partial Fractions 2.8.2Partial Fractions with Three Linear Factors 2.8.3Partial Fractions with Three Linear Factors 2 2.8.4Partial Fractions with Repeated Factors 2.8.5Partial Fractions - Practice

3

Coordinate Geometry

3.1

Straight Lines

3.1.1y = mx +c 3.1.2Gradient & Y-intercept 3.1.3Distance-Time Graph 3.1.4Velocity-Time Graph 3.1.5Conversion Graph

3.2

Circles

3.2.1Equations of Circles centred at Origin 3.2.2Finding the Centre & Radius 3.2.3Equation of a Tangent 3.2.4Circle Theorems - Perpendicular Bisector 3.2.5Circle Theorems - Angle at the Centre 3.2.6Circle Theorems - Angle at a Semi-Circle 3.2.7Equation of a Perpendicular Bisector 3.2.8Equation of a Circumcircle 3.2.9Circumcircle of a Right-angled Triangle

3.3

Parametric Equations (A2 only)

3.3.1Parametric Equations 3.3.2Modelling with Parametric Equations

4

Sequences & Series

4.1

Binomial Expansion

4.1.1Pascal's Triangle 4.1.2Factorials 4.1.3Binomial Expansion 4.1.4Binomial Expansion & Rational Powers (A2 only)4.1.5Binomial Expansion & Rational Powers 2 (A2 only)

4.2

Sequences (A2 only)

4.2.1Nth term Rules 4.2.2Recurring Rules 4.2.3Types of Sequences 4.2.4Arithmetic Sequences 4.2.5Geometric Sequences 4.2.6Sigma Notation 4.2.7Arithmetic Series 4.2.8Geometric Series 4.2.9Sum to Infinity of a Geometric Series 4.2.10Modelling with Sequences & Series

5

Trigonometry

5.1

Using Angles

5.1.1Radians 5.1.2Arc length 5.1.3Area of Sectors 5.1.4Area of Segments

5.2

Trigonometric Functions

5.2.1Unit Circle 5.2.2Properties of Trig Functions 5.2.3Trigonometry 5.2.4Exact values 5.2.5Graphs of Trigonometric Functions 5.2.6Small Angle Approximation

5.3

Triangle Rules

5.3.1Sine Rules 5.3.2Cosine Rules 5.3.3Area of a Triangle

5.4

Trigonometric Identities

5.4.1Secant, Cosecant & Cotangent 5.4.2Pythagorean Identities 5.4.3Angle Addition Formulae 5.4.4Manipulating the Angle Addition Formulae 5.4.5Double Angle Formula

6

Exponentials & Logarithms

6.1

Exponentials & Logarithms

6.1.1Exponential Function 6.1.2Logarithms 6.1.3Properties of Logarithms 6.1.4Natural Logarithm 6.1.5Graphs of Exponents & Logarithms

6.2

Exponential Growth Decay

6.2.1Population Growth 6.2.2Depreciation 6.2.3Graphing Linear and Exponential Growth 6.2.4Interpreting Exponential Growth and Decay Graphs 6.2.5Compound Growth & Decay 6.2.6Compund Interest

7

Differentiation

7.1

Derivatives

7.1.1Gradient of a Curve 7.1.2Differentiation from First Principles 7.1.3Differentiation from First Principles - Practice 7.1.4Differentiation 7.1.5Finding derivatives 7.1.6Second Order Derivatives

7.2

Graphs & Differentiation

7.2.1Stationary Points 7.2.2Maxima & Minima 7.2.3Modelling with Differentiation 7.2.4Using Second Derivatives (A2 only)7.2.5Rate of Change (A2 only)

7.3

Differentiation With Trigonometry and Exponentials

7.3.1Differentiation with Sin & Cos 7.3.2Diff. of Exponential Functions 7.3.3Differentiation of Trig. Functions 1 (A2 only)7.3.4Differentiation of Trig. Functions 2 (A2 only)

7.4

Rules of Differetiation (A2 only)

7.4.1Chain Rule 7.4.2Product Rule 7.4.3Quotient Rule

7.5

Parametric & Implicit Differentiation

7.5.1Parametric Differentiation 7.5.2Implicit Differentiation

8

Integration

8.1

Integration

8.1.1Integration - Basics 8.1.2Integration - Definite Integrals 8.1.3Finding Functions 8.1.4Area under curves 8.1.5Area under x-axis 8.1.6Area between curves and lines

8.2

Integration (A2 Only)

8.2.1Integration - Standard Functions 8.2.2Integration - Reverse Chain Rule 8.2.3Integration by Substitution 8.2.4Integration by Parts 8.2.5Integration by Parts - Practice 8.2.6Integration by Partial Fraction 8.2.7Modelling with Differential Equations

9

Numerical Methods

9.1

Finding Solutions

9.1.1Number Iterations 9.1.2Iterations to 1 Decimal Places 9.1.3Iteration Formula 9.1.4Locating Roots 9.1.5Newton Raphson Method

9.2

Finding the Area

9.2.1Trapezium Rule

10

Vectors

10.1

2D Vectors

10.1.1Vectors - Magnitude & Direction 10.1.2Unit Vectors 10.1.3Vectors - Algebraic Operations 10.1.4Position Vectors 10.1.5Vector Proofs 10.1.6Vectors Word Questions

10.2

3D Vectors

10.2.13D Vector Magnitude 10.2.23D Vectors - Algebraic Operations 10.2.3Position Vectors 3D 10.2.43D Vectors Word Questions

10.3

Vector Proofs

10.3.1Coming Soon

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Mathematical Proof

Proving an Identity