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Dynamic Geometry: Langley's Problem, Isosceles Triangle, 20, 50, 60, 80 Degrees, Angle. HTML5 Animation for Mobile Devices. Click the Next button below to start the step-by-step solution.

In an isosceles triangle ABC (AB = BC), E is on AB and D is on BC. If angle B = 20 degrees, angle DAC = 60 degrees, and angle ACE = 50 degrees, find the measure of angle ADE. Click the next (play) button below to start.

The famous Langley problem is a type of problem called "Adventitious Angles" problem because it is a matter of chance that we will be able to solve this problem (drawing auxiliary lines). It appears to be an easy problem, but it is deceivingly difficult.

  • Reference: The Mathematical Gazette, UK

  • Author: Edward M. Langley

  • Title: A problem

  • Page: 173

  • Issue: October 1922

  • Category: M Note 644

   See also: Artwork of Langley's problemJigsaw Puzzle: Langley's Problem: 40 Quadrilateral Pieces

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Last update Jun 30, 2016 by Antonio Gutierrez