Online Course Discussion Forum
Math Challenge II-A Geometry 7.17
Why is the answer 120 degrees? I wrote 60 degrees. If the question was asking the size of the central angle of arc AC, then it should be 120 degrees. However, it is asking the size of the central angle of arc AB, which should be 60 degrees because that’s the measure of an angle in an equilateral triangle. Since OA is parallel to BC, then A and B must be adjacent, therefore shouldn’t the answer be 60 degrees?
Why does OA parallel to BC imply that A and B must be adjacent? Here the question is asking about quadrilateral OACB, which implies that actually points A and C are adjacent.
I think you interpreted points B and C swapped, which does give an answer of 60 degrees instead of the 120 degrees which is implied by looking at quadrilateral OACB.
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