10th Class Mathematics Circles Question Bank Circle

  • question_answer
    A quadrilateral ABCD is drawn to circumscribe a circle (see figure). Then

    A)  \[~AB+CD=AD+BC\]

    B)  \[AB+AC=BC+BD\]

    C)  \[AB+BC=CD+DA\]

    D)  \[AB+BD=BC+CA\]

    Correct Answer: A

    Solution :

    (a): Using theorem, the lengths of tangents drawn from an external point to a circle are equal. A is an external point, then AP = AS  .... (i) B is an external point, then BP = BQ .... (ii) C is an external point, then CQ = RC .... (iii) D is an external point, then SD = RD .... (iv) On adding Eq. (i), (ii), (iii) and (iv), we get \[\left( AP+BP \right)+\left( RC+RD \right)\] \[=\left( AS+BQ \right)+\left( CQ+SD \right)\] \[\Rightarrow \]\[AB+CD=\left( AS+SD \right)+\left( BQ+CQ \right)\] \[\Rightarrow \]\[AB+CD=AD+BC\]


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