Unjustified Assumptions Based on Diagrams in Geometry

Tali Dvora, Tommy Dreyfus

Research output: Book/ReportReport


We investigated unjustified assumptions made by students when proving geometric statements. Geometric statements can be presented with a diagram or without. Diagrams can be accurate or sketchy. Unjustified assumptions may originate in an accompanying diagram. We thus asked whether the way in which a statement is presented has an effect on unjustified assumptions. We also attempted to find out what motivates students to make unjustified assumptions. Data were collected by means of written questionnaires and individual interviews. The main findings were that among all incorrect answers, 72% were based on unjustified assumptions, and that students make unjustified assumptions with good reasons such as in order to remove obstacles. [For complete proceedings, see ED489632.]
Original languageEnglish
Place of PublicationBergen, Norway
PublisherInternational Group for the Psychology of Mathematics Education
Number of pages8
StatePublished - Jul 2004


  • ERIC, Resources in Education (RIE)
  • High Schools
  • Students
  • Geometry
  • Student Motivation
  • Task Analysis
  • Mathematics Instruction
  • Geometric Concepts
  • Questionnaires
  • High School Students
  • Interviews


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