Learning mathematical proof, lessons learned and outlines of a learning environment

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SDSU seminar, 2005 This talk outlined aspects of learning mathematical proof and presented the principles of the design of a learning environment (V. Luengo PhD 1997)

Transcript of Learning mathematical proof, lessons learned and outlines of a learning environment

© N. Balacheff Oct. 2005

Learning mathematical prooflesson learned from research

&principles of design of a learning environment

Nicolas.Balacheff@imag.fr

© N. Balacheff Oct. 2005

A controversial question...

What is a mathematical proof ?

© N. Balacheff Oct. 2005

The rôle of mathematical proofin the practice of mathematicians

Internal needs

Social communication

© N. Balacheff Oct. 2005

The rôle of mathematical proofin the practice of mathematicians

Internal needs

Social communication

mathematicalrationalism

non mathematicalrationalismVersus

© N. Balacheff Oct. 2005

The rôle of mathematical proofin the practice of mathematicians

Internal needs

Social communication

mathematicalrationalism

non mathematicalrationalismVersus

VersusRigour Efficiency

© N. Balacheff Oct. 2005

The rôle of mathematical proofin the practice of mathematicians

Internal needs

Social communication

mathematicalrationalism

non mathematicalrationalismVersus

VersusRigour Efficiency

The specific economyof the practice of mathematics

© N. Balacheff Oct. 2005

Argumentationvs

Mathematical proof

Argumentation

            content count

            epistemic value

Mathematical proof

            operational value count

            structural value

© N. Balacheff Oct. 2005

Mathematical proof can be considered as an answer to...

The search for certainty

The need for communication

The search for understanding

© N. Balacheff Oct. 2005

Mathematical proof can be considered as an answer to...

The search for understandingThe search for certainty

The need for communicationYes, and the three

dimensions cannot be separated....

© N. Balacheff Oct. 2005

Learning mathematical proof,which genesis ?

the origin of knowledge is in actionbut the achievement of

Mathematical proof is in language

© N. Balacheff Oct. 2005

Learning mathematical proof,which genesis ?

the origin of knowledge is in actionbut the achievement of

Mathematical proof is in language

knowledge in action

knowledge in discourse

© N. Balacheff Oct. 2005

Learning mathematical proof,which genesis ?

the origin of knowledge is in actionbut the achievement of

Mathematical proof is in language

knowledge in action

knowledge in discourse

         construction

© N. Balacheff Oct. 2005

Learning mathematical proof,which genesis ?

the origin of knowledge is in action

© N. Balacheff Oct. 2005

Learning mathematical proof,which genesis ?

the origin of knowledge is in action

© N. Balacheff Oct. 2005

Learning mathematical proof,which genesis ?

the origin of knowledge is in action

© N. Balacheff Oct. 2005

Learning mathematical proof,which genesis ?

the origin of knowledge is in action

© N. Balacheff Oct. 2005

Learning mathematical proof,which genesis ?

the origin of knowledge is in action

© N. Balacheff Oct. 2005

Learning mathematical proof,which genesis ?

the origin of knowledge is in action

Yes, but...why is that true ?

© N. Balacheff Oct. 2005

Learning mathematical proof,which genesis ?

the origin of knowledge is in action

© N. Balacheff Oct. 2005

formulationnature of

knowledgevalidation

© N. Balacheff Oct. 2005

formulationnature of

knowledgevalidation

demonstration

practice(know how)

Pragmaticproofs

© N. Balacheff Oct. 2005

formulationnature of

knowledgevalidation

demonstration

language of afamiliar world

practice(know how)

Pragmaticproofs

© N. Balacheff Oct. 2005

formulationnature of

knowledgevalidation

demonstration

language of afamiliar world

language asa tool

practice(know how)

explicitknowledge

Pragmaticproofs

© N. Balacheff Oct. 2005

formulationnature of

knowledgevalidation

demonstration

language of afamiliar world

language asa tool

naïveformalism

practice(know how)

explicitknowledge

knowledgeas a theory

Pragmaticproofs

Intellectualproofs

© N. Balacheff Oct. 2005

formulationnature of

knowledgevalidation

language

conceptualization

control

© N. Balacheff Oct. 2005

The origin of knowledge is in problems

in the case of proof, mathematical problem-solving is not enough

the need to stimulate a movementfrom proof as a tool to proof as an object

contradictions as means to give rise to the problem of proof

counter-examplesa revealers

socio-cognitifconflicts as catalysts

© N. Balacheff Oct. 2005

The origin of knowledge is in problems

in the case of proof, mathematical problem-solving is not enough

the need to stimulate a movementfrom proof as a tool to proof as an object

contradictions as means to give rise to the problem of proof

counter-examplesa revealers

socio-cognitifconflicts as catalysts

counter-examplesa

revealers

© N. Balacheff Oct. 2005

Counter-examples as revealers

Let ABCD be a parallelogram, A’ the symetric image of Awith respect to point B, B’ the symetric image of ...

A’B’C’D’ isa parallelogram

© N. Balacheff Oct. 2005

Counter-examples as revealers

Let ABCD be a parallelogram, A’ the symetric image of Awith respect to point B, B’ the symetric image of ...

A’B’C’D’ isa parallelogram

SAS

© N. Balacheff Oct. 2005

Counter-examples as revealers

Let ABCD be a parallelogram, A’ the symetric image of Awith respect to point B, B’ the symetric image of ...

A’B’C’D’ isa parallelogram

SAS

He!What about a square ? !

© N. Balacheff Oct. 2005

Counter-examples as revealers

Let ABCD be a square...

A’B’C’D’ is alsoa square

© N. Balacheff Oct. 2005

Counter-examples as revealers

Let ABCD be a square...

A’B’C’D’ is alsoa square

This is great!It holds!

© N. Balacheff Oct. 2005

Counter-examples as revealers

So, let ABCD be a rectangle...

A’B’C’D’ is NOTa rectangle

© N. Balacheff Oct. 2005

Counter-examples as revealers

So, let ABCD be a rectangle...

A’B’C’D’ is NOTa rectangle

Too bad!So what?

© N. Balacheff Oct. 2005

How to deal with a counter-example?

The mathematics classroom tends to be a manichean world:

to be or not to be true is the only question

Whereas an example proves mathematically nothing, a counter-example just destroyes every effort...

Could we revisit the old classical position?

© N. Balacheff Oct. 2005

ProofConjecture

© N. Balacheff Oct. 2005

ProofConjecture

Counter-example

© N. Balacheff Oct. 2005

ProofConjecture

Counter-example

The Lakatosiannightmare, again...

© N. Balacheff Oct. 2005

ProofConjecture

Rationality Knowledge

Counter-example

© N. Balacheff Oct. 2005

ProofConjecture

Rationality Knowledge

Counter-example

© N. Balacheff Oct. 2005

Where are we?

A constructivist approach is possible, but a problématiqueof proof must not be separated from knowledge construction

Regulation of cognitive processesrelated to proving in mathematics,treatment of refutations

© N. Balacheff Oct. 2005

Where are we?

A constructivist approach is possible, but a problématiqueof proof must not be separated from knowledge construction

Regulation of cognitive processesrelated to proving in mathematics,treatment of refutations

Specific situations are needed in order to elicitthe meaning of mathematical proofs

The rôle of the teacher, negociationnot on the objects but on the means

© N. Balacheff Oct. 2005

Computer-based microworldscould offer a virtual reality tomathematical abstractions

Where are we?

A constructivist approach is possible, but a problématiqueof proof must not be separated from knowledge construction

Regulation of cognitive processesrelated to proving in mathematics,treatment of refutations

Specific situations are needed in order to elicitthe meaning of mathematical proofs

The rôle of the teacher, negociationnot on the objects but on the means

Mathematics needs a specific milieu which feedbackcan reflect the specificities of its objects

© N. Balacheff Oct. 2005

Computer-based microworldscould offer a virtual reality tomathematical abstractions

Where are we?

A constructivist approach is possible, but a problématiqueof proof must not be separated from knowledge construction

Regulation of cognitive processesrelated to proving in mathematics,treatment of refutations

Specific situations are needed in order to elicitthe meaning of mathematical proofs

The rôle of the teacher, negociationnot on the objects but on the means

Mathematics needs a specific milieu which feedbackcan reflect the specificities of its objects

Computer-basedmicroworldscould offer avirtual reality tomathematicalabstractions

© N. Balacheff Oct. 2005

Knowledge as the equilibrium state of a

Subject/Milieu System

S M

action

feedback

Which characteristics for M in the case of mathematics?

© N. Balacheff Oct. 2005

S M

action

feedback

The limits of the “real” world

© N. Balacheff Oct. 2005

S M

action

feedback

The limits of the “real” world

N°16 - The rainwater from a flat roof 15m by 20m drains into a tank 3m deep on a base 4 m square. What depth of rainfall will fill the tank...(O level, 1978)

© N. Balacheff Oct. 2005

A domain of phenomenology

A formal system

S M

action

feedback

The limits of the “real” world

The potential of computer-based environments

© N. Balacheff Oct. 2005

A domain of phenomenology

A formal system

S M

action

feedback

The limits of the “real” world

mathematical properties as perceptual phenomena

computational representation of objects and relations

The potential of computer-based environments

© N. Balacheff Oct. 2005

A domain of phenomenology

A formal system

S M

action

feedback

direct manipulation of graphical objects

formal objects and relationships, a cartesian model

The case of geometry

© N. Balacheff Oct. 2005

The case of geometry

Cabri-géomètre, a dynamic geometry software

© N. Balacheff Oct. 2005

The case of geometry

Cabri-géomètre, a dynamic geometry software

Construct the symmetrical point P1 of P about A,then the symmetrical point P2 of P1 about B, etc. Then, construct the point I, the midpoint of [PP3].

What can be said about the point I when P is moved?

© N. Balacheff Oct. 2005

The case of geometry

Cabri-géomètre, a dynamic geometry software

I move P and I does not move.When, for example, we put P to the left,then P3 compensate to the right.If it goes up, then the other goes down...

© N. Balacheff Oct. 2005

Learning mathematical proof,which genesis ?

the origin of knowledge is in actionbut the achievement of

Mathematical proof is in language

knowledge in action

knowledge in discourse

         construction

© N. Balacheff Oct. 2005

TheoreticalGeometry

PracticalGeometry

© N. Balacheff Oct. 2005

TheoreticalGeometry

PracticalGeometry

geometrical figure

satisfiabilitytheoretical existence

© N. Balacheff Oct. 2005

TheoreticalGeometry

PracticalGeometry

geometrical figure

geometrical drawing

satisfiability

constructibility

theoretical existence

effective construction

© N. Balacheff Oct. 2005

TheoreticalGeometry

PracticalGeometry

geometrical figure

geometrical drawing

satisfiability

constructibility

theoretical existence

effective construction

rules of the art

mathematical proof

© N. Balacheff Oct. 2005

TheoreticalGeometry

PracticalGeometry

geometrical figure

geometrical drawing

satisfiability

constructibility

theoretical existence

effective construction

rules of the art

mathematical proof

© N. Balacheff Oct. 2005

TheoreticalGeometry

PracticalGeometry

geometricalobject

geometrical figure

geometrical drawing

satisfiability

constructibility

theoretical existence

effective construction

rules of the art

mathematical proof

© N. Balacheff Oct. 2005

The end?

© N. Balacheff Oct. 2005

Learning mathematical proof,which genesis ?

the origin of knowledge is in actionbut the achievement of

Mathematical proof is in language

in a mathematical microworld

for a rational agent, understanding the constraints of the mathematical discourse

V. Luengo 1997

From action...

... to formulation

© N. Balacheff Oct. 2005

© N. Balacheff Oct. 2005

DrawingDrawing

© N. Balacheff Oct. 2005

DrawingDrawingTextText

© N. Balacheff Oct. 2005

DrawingDrawingTextText

StructureStructure

© N. Balacheff Oct. 2005

© N. Balacheff Oct. 2005

This property appears to be true on your drawing,but it is not the case in general;

would you like a counter-example

© N. Balacheff Oct. 2005

© N. Balacheff Oct. 2005

The statement “[AC] is parallel to [KL]”cannot be obtained using this theorem.

© N. Balacheff Oct. 2005

© N. Balacheff Oct. 2005

The proof is correct but you have to provethe remaining conjectures

© N. Balacheff Oct. 2005

The (very) end!