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Circle theorum GCSE help please!!!! watch

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    Hi. Please see attached question. I have almost no clue about how to answer these questions! Quite worrying really considering my exam is on tuesday :eek: I think that part (a) might be 40 because it's half of BOC, but I'm not too sure. Please could someone explain how to do the question. Thanks
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    you were right for the first one - 40 degrees

    unfortunately i couldn't work out last one.
    solutions attached
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    The first part u got it correct. Now the second...


    OBA = 12

    since: there's a theorem equating ABC with DAC angles. Now the triangle OBC is isoceles so OBC = (180-80)/2 = 50

    OBA = OBC - ABC = 12

    Now for the last part it is quite easy since for the given circle to exist it is neccessary for angle EAD to be equal to 90 degrees, but it's not since

    EAD = 40 + 38 = 78
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    but how can angle OBA=12 because triangle OBA is icoseles, no?

    EDIT: Ignore that comment, I just realised how dumb i am
 
 
 
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Updated: June 3, 2005

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