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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?

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figure

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).