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For family of circles whose inscribed angle makes an angle of $ \theta$ with a line segment is given as: enter image description here If the coordinate of $E=(x_1,y_1)$ and of $B=(x_2,y_2)$ then the family of circles for which $EBH$ makes an angle $\theta$ (here 53) is given as: $$(x-x_1)(x-x_2) + (y-y_1)(y-y_2) \pm \cot \theta \left[ (x-x_1)(y-y_2) - (x-x_2)(y-y_1)\right]$$

This result was given a JEE book (Famous Indian engineering exam) with no explanation why this is true, could any one shed light on why this formula represents what it is supposed to?

  • @Pravimish all points standing on the same arc make the same angle for a given circle of radius, look up inscribed angle theorem. Else, explain why you think it's wrong – tryst with freedom Feb 06 '21 at 21:07
  • sry for the confusion, ihave deleted the comment – Pravimish Feb 07 '21 at 09:01
  • Also, can u give some clarity on the following thought. U have a fixed line segment EB. If this always forms an angle of $53^{\circ}$, then isnt there only one possible triangle, ergo, one possible circle. – Pravimish Feb 07 '21 at 09:05
  • take a point further outside, that would make a different angle while standing on the same arc, no? Now apply the inscribed angle thinking to that point as well @Pravimish – tryst with freedom Feb 07 '21 at 10:09

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