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@ErinWeeks We should never guess in math, or else you will always have 25% or thereabouts for your grades! :(
The above diagram shows the relation between the angles subtended by the same chord AC, at the circumference B or at the centre O.
If you join OB, then OA,OB,OC are all equal to the radius. Thus triangl OAB is isosceles, therefore mBAO=mABO. Similarly mBCO=mCBO.
But mABO+mCBO=mAOC (exterior angles), which means finally
\( mAOC=2 * mABC.\)
Hope this helps.
Note: this is similar to the question I answered previously. Hope that this more detailed explanation helps you work on other problems.
Please, do NOT guess your answers if you want a good grade. Understanding is faster than guessing.