The user-friendly version of this content is available here.
The following content is copyright (c) 2009-2013 by Goods of the Mind, LLC.
This problem trains for: SAT-I.
In a circle of radius R = 10 three different diameters are drawn. What is the sum of the non-adjacent angles formed?
Each of the marked angles is congruent to the angle that is vertical to it. Since each of the marked angles has a 'twin', the non-adjacent angles add up to 180° regardless of the choice of diameters (provided they are different).