Online Course Discussion Forum

Math Challenge II-A Geometry 7.17

 
 
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Math Challenge II-A Geometry 7.17
by Zeyin Wu - Tuesday, 26 October 2021, 3:38 AM
 

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?

 
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Re: Math Challenge II-A Geometry 7.17
by John Lensmire - Tuesday, 26 October 2021, 11:50 AM
 

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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回复: Re: Math Challenge II-A Geometry 7.17
by Zeyin Wu - Tuesday, 26 October 2021, 3:17 PM
 

Oh I see. Thanks