<Dd> A B C D = I A ⋅ I B I C ⋅ I D, B C D A = I B ⋅ I C I D ⋅ I A . (\ displaystyle (\ frac (AB) (CD)) = (\ frac (IA \ cdot IB) (IC \ cdot ID)), \ quad \ quad (\ frac (BC) (DA)) = (\ frac (IB \ cdot IC) (ID \ cdot IA)).) </Dd> <P> The product of two adjacent sides in a tangential quadrilateral ABCD with incenter I satisfies </P> <Dl> <Dd> A B ⋅ B C = I B 2 + I A ⋅ I B ⋅ I C I D . (\ displaystyle AB \ cdot BC = IB ^ (2) + (\ frac (IA \ cdot IB \ cdot IC) (ID)).) </Dd> </Dl> <Dd> A B ⋅ B C = I B 2 + I A ⋅ I B ⋅ I C I D . (\ displaystyle AB \ cdot BC = IB ^ (2) + (\ frac (IA \ cdot IB \ cdot IC) (ID)).) </Dd>

How to find the perimeter of a quadrilateral with a circle inside