Quandaries and Queries


Show that the peints A(-2,0),B(6,6),C(-1,7) and D(-2,6) are concyclic. Also find its circum radius.



You need to compute some angles: for a quadrangle to be cyclic the opposite angles must be supplementary. For R you can use the sine law in any of the triangles: 2R equals the ratio a/sin A (= the ratio of a side of a TRIANGLE to the sine of the opposite angle).



Go to Math Central