8 thoughts on “Circles and Quadrilaterals

  1. Dear J,
    Do i need to remember the proofs of the theorems ? I mean is there any chance that the concept applied to prove the theorem be used to solve any other geometry question ( any question , for that matter , not related to the theorem itself ) ?

  2. You don’t need to “remember” the proof. At least, not in the way we were supposed to in school (mug it up, step by step). However I would recommend going through and understanding the proofs (and preferably being in a position where you can prove any of the theorems from scratch, though that is optional).

    The reason being that only if you understand the reasoning behind the proof of a formula/statement/theorem then you will (a) be able to recognise and visualise correctly where to apply it and (b) ensure that you don’t apply any random proof anywhere, i.e. know where it can *not* be applied.

    Many of the most embarrassing mistakes in Geometry tend to happen when one applies a theorem somewhere where it is not applicable – just yesterday I came across two such beauties – one person who was trying to apply Brahmagupta’s formula for the area of a cyclic quadrilateral [sqrt(s-a)(s-b)(s-c)(s-d)] for some random quadrilateral and another who was using 1/2 * (product of diagonals) for a rectangle….


  3. HI sir, the last property- angle bisectors being concurrent, at the centre of circle, i havent really come across a question where this property is used, or maybe we use this property but not in this form.
    Could you please help me understand how and in what type of questions do we use this? or is it only for our understanding purpose?

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