If A is the center of the circle shown above and AB = BC

BTGmoderatorLU wrote:Source: GMAT Paper Tests



If A is the center of the circle shown above and AB = BC = CD, What is the value of x?

A. 15
B. 30
C. 45
D. 60
E. 75

The OA is B.

First recognize that all radii (indicated with BLUE lines) have equal length


Since BC and CD are both equal to the radius AB, we can see that all BLUE lines have equal length


This means the 2 blue triangles are EQUILATERAL triangles, which means all angles = 60°


All we really need answer the question is that these 2 angles are 60° each


This means we have an ISOSCELES triangle with a 120° angle


Since we have an ISOSCELES triangle, the two remaining angles must be 30° each (since all angles must add to 180°


Answer: B

Cheers,
Brent