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

  • Graph of Slopes of Tangent Lines
  • apec
  • Limaçons
  • The Geometry of the Coefficients of a Quadratic Function
  • Taylor Error Bound

Discover Resources

  • undefined
  • Untitled_777
  • Graf dráhy v závislosti na čase
  • Gradniki življenja
  • Construct triangles 3 sides variable

Discover Topics

  • Kite
  • Planes
  • Tangent Function
  • Hypergeometric Distribution
  • Sphere
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®