Circumscribed quadrilateral

[ins-]

It is given a convex a circumscribed quadrilateral ABCD. In the triangles ACB, ACD, BDA, BDC are inscribed circles with radii: $r_1$, $r_2$, $r_3$, $r_4$. Is it always true that:
a) $r_1r_2=r_3r_4$
b) $r_1+r_2=r_3+r_4$
c) $\frac{1}{r_1}+\frac{1}{r_2}=\frac{1}{r_3}+\frac{1}{r_4}$
?

[Dimoniada]

a) -
b) -
c) -

[ins-]

Thank you. I asked because of the following problem:
http://www.math10.com/f/viewtopic.php?f=49&t=1756
I'm wondering if there any dependency between inradii i mentioned.
You are correct i verified in the train.