A line meets the co-ordinate axes in A & B, a circle is circumscribed about the triangle OAB. If d1 and d2 are the distances of the tangent to the circle at the origin O from the points A and B respectively the diameter of the circle is:
AL = d1
BM = d2
The line joining the midpoints of non-parallel sides of a trapezium is parallel, to then parallel sides and half of the sum of the parallel sides.
r=12(d1+d2)
2r=d1+d2