Search
GeoGebra
  • Home
  • Resources
  • Profile
  • Classroom
  • App Downloads

Lesson 86. Properties of Parallel Lines

Author:Norm Prokup

T6-criterion for parallel lines

[bgcolor=orange] If two lines are intersected by a third line, and alternate interior (or exterior) angles are equal, then the original two lines are parallel. [/bgcolor]

New Resources

  • גיליון אלקטרוני להעלאת נתוני בעיה ויצירת גרף בהתאם
  • bewijs stelling van Pythagoras
  • Shells
  • Reflection across a line
  • Equation of Locus - Parabola

Discover Resources

  • Lesson 15 Parallels
  • leftHandTrig_4_2a
  • Juggling in an equilateral triangle - route 3
  • Right Triangle to Circle Demo
  • Nets of 3D solids
  • PeterRhombus

Discover Topics

  • Diagrams
  • Differential Calculus
  • Equilateral Triangles
  • Curve Sketching
  • Boxplot
AboutPartnersHelp Center
Terms of ServicePrivacyLicense
Graphing CalculatorCalculator SuiteMath Resources

Download our apps here:

Download_on_the_App_Store_Badge_US-UK_RGB_blk_4SVG_092917

© 2026 GeoGebra®